To qualify for participation, subjects are to be between the ages of 18-55, medically healthy and free of all medication three months prior to enrollment. Half of them will be clinically depressed; the remaining one half will be healthy controls without a history of psychiatric illness. All subjects who qualify for the study will attend two laboratory sessions. During the first visit, participants will undergo a structured psychological interview, complete questionnaires about their mood, personality, and behavior, and have blood drawn to assess their immune system function. During the second visit, participants will complete additional questionnaires about their mood, personality, and behavior. The subjects will also participate in a mock job interview to look at their body's response to stress. Before and after the interview, the subjects will have blood drawn and be asked to collect saliva samples to assess their immune system function. In addition to the two laboratory visits, participants will be asked to collect additional information while going about their normal activities. In order to accomplish this, they will be given a small hand held portable computer. Four times each day for four days, the computer will signal them to collect a saliva sample. This will be used later to measure hormone levels. This study will explore changes in the immune system and metabolic system that might predispose depressed individuals to develop heart disease