A medical researcher, despondent when his grandson's decides to become a professional athlete rather than follow in his footsteps refuses treatment for a fatal form of malaria so Welby hires a headstrong nurse to enforce treatment.
An impoverished Appalachian family have moved to Los Angeles looking for work but they are hesitant to get medical treatment for looming health problems because tradition says to not accept anything they can't pay for.
Nancy Riggs has been in remission for her leukemia for six years and with the blessing of Welby and her oncologist wants to move back into the outside world but her father wants to keep her in a sterile cocoon the rest of her life.
An aspiring race car driver refuses to find out what is causing severe headaches because it may endanger his career but the headaches send him into uncontrollable fits of rage that endanger him and everyone around him.
The mother of a young boy is a strong believer in a religious group called The Satan Fighters. When he becomes fatally ill, she believes he is being taken by his guardian angel to heaven and refuses medical treatment to allow this miracle to happen. Dr. Welby must do everything in his power to save the boy.
Life outside the ring - permanently - is not easy for Danny Williams, a promising young fighter who shields the fact that he is epileptic from his wife. Williams struggles with having to adjust to a new life, despite the best efforts of Welby, Kiley and Williams' wife, Laurie.
A young couple has a daughter who has unexplained attacks and keeps her hidden. Welby and Kiley diagnose her as having tortion dystonia, a disease similar to muscular dystrophy. The surgical process to releave her symptoms is shown.
Dr. Welby's patient dies in the night and her daughter agrees, under grieving duress, to a $5000 funeral. In the meantime, Dr. Kiley's long-time friend develops problems with his kidneys, and is unable to attend the opening of his art exhibit. Not to worry, Marcus Welby, M.D. is on both cases!