Diagnosis: Murder (season 4)

A friend of Steve's winds up dead in a friendly-fire incident involving a veteran cop, but the shooting may have been planned all along. Kim Johnston Ulrich played the conniving widow. Guest Star: Jonathan Banks.

Sloan and Jesse make contact with a patient who died from a genetically altered strain of smallpox. Steve and Amanda only have hours to find the cure before it's too late.

After faking an attack on herself just to win endorsements, a skater kills her accomplice and frames her rival.

A string of murders occurs with the same killer signature. One of the victims supposedly called Mark, but it is after she was known to be dead. The case becomes personal when the killer starts calling Mark. Mark gets involved in the string of murders when the killer starts calling Mark. It gets more personal when the killer attacks Amanda. She manages to escape. Mark and Steve get closer to finding the killer. After the killer claims he didn't kill one of the victims, Mark and Steve look for the copycat murderer.

Sloan and Steve investigate a fashion show when they suspect a modeling agent of being a serial killer who murdered a private eye that discovered her secret, and her next target is one of Jesse's college buddies.

A cardiologist (Alan Rachins) and two business partners concoct a devious insurance scam to murder a man and pass him off as one of them, but when the partner who was supposed to be dead gets cold feet, he is murdered for real. Meanwhile, Mark adopts a basset hound belonging to one of Jesse's deceased relatives, as the others try to find a home for it.

An ambitious female cop who idolizes Steve tracks a terrorist (Eric McCormack) who blew up a delivery truck and killed the driver, injuring Mark in the process. When the terrorist orders a hit on Mark, the cop must make a difficult choice.

A bus crashes after T-boning a drunk driver. All of the passengers survive the accident, but one of them, an insurance adjuster and a rapist, is murdered in the aftermath, which is discovered by Mark when he is brought in to the hospital. The only suspects are the other passengers on the bus; a homeless ex-soldier with hallucinations of Vietnam, a college student who was the victim's next rape target, the widower of a cancer patient who fell into debt due to the victim scamming him into buying a phony policy, and a woman who is a master of insurance fraud. As Mark tries to make sense of what happened, the soldier is murdered as well, and now Mark is down to three suspects, none of whom seem to have been able to commit either murder. But a reexamination of the crime scene and an autopsy of the Soldiers reveals an unexpected culprit. In a subplot, the accident and murder cause Mark and Steve to miss a Lakers game, and the coach arrives to give them free tickets to the next game as a token of appreciation for their service. However, Amanda tears them up because the coach is a friend of the fraud-loving woman, believing they're fakes.

The drug-addicted daughter of a senator is killed during an argument, but a senior aide tries to make it look like an overdose. However when the autopsy reveals inconsistencies, Mark discovers just how far the aide will go to protect the Senator's career.

Sloan helps a district attorney (Piper Laurie) probe a drive-by shooting at a high school which left a popular teacher dead. But her stubborn insistence that a Korean teen is responsible makes finding the real killer a challenge. Guest Star: Piper Laurie.

Mark's daughter, Carol Hilton (Stacy Van Dyke) comes home for Christmas in an attempt to escape the wrath of her abusive trucker husband Bruce. She plans to file for divorce and move upstate for a new job, but before she can put her plan into action, Bruce is murdered. Unbeknownst to Carol, Bruce's actual job was illegally dumping toxic waste and blackmail, and she's likely the next target.

Sloan looks for clues to solve the decades-old murder of his mentor (Nicholas Pryor), when his body is found during hospital renovations, but another murder in the present disrupts his attempts.

Sloan enlists his friend Ben Matlock (Andy Griffith) to defend Jesse, who's accused of murdering a resident. Guest Star: Lee Chamberlin.

With Jesse falsely accused of murdering Eric Spindler, Ben Matlock (Andy Griffith) gathers all the evidence to find the real killer. Guest Star: H. Richard Greene. Note: This was Andy Griffiths final appearance as Ben Matlock

Sloan assists Joe Mannix (Mike Connors) with an unsolved murder case from 1973.
Note: This episode serves as a sequel to the Mannix episode "Little Girl Lost". Guest Stars: Richard Gant, Julie Adams, Pernell Roberts, and Beverly Garland.

The prime suspects in the murder of a country star are a driven TV producer and her timid songwriter daughter. Guest Stars: Deanne Bray, Barbara Mandrell, Billy Ray Cyrus, Terri Clark, Linda Davis, Billy Dean, Joe Diffie, Eddie Rabbitt, and Reba McEntire.

Psychiatrist Gavin Reed (Dwight Schultz) kills his estranged wife Claire (Teri Austin) and tries to frame a patient. But Mark and Amanda suspect otherwise and they soon learn Reed has sinister motives with his patients. Guest Stars: Dwight Schultz.

A beach boy is suspected of killing his girlfriend's brother – a gang member. Guest Stars: Carey Van Dyke, and Shane Van Dyke.

A surgeon drops dead while operating on another doctor.

A wealthy woman, Claire Whitfield (Brynn Thayer) and her lover cook up an elaborate plot to bump off her husband, Elliott (Wayne Tippit) and frame Mark. Brynn Thayer plays Leanne Macintyre on Matlock.

A washed up comedian stumbles in his attempts to murder his more successful partner, whose ex-wife ends up dead in the pool. But evidence soon suggests he might not be responsible. Guest Stars: Harvey Korman, Tim Conway (plays Tim Conrad), and Tom Gallop (plays Phil Zarkin).

A mad bomber whom Sloan helped put away breaks out of prison bent on revenge, but Mark discovers the bomber was not responsible for all attempts on his life. Guest Stars: Carol Bruce, and Mary Kay Adams.