This protocol presents the rationale, 25-year historical review, and methods for multidisciplinary, low-risk studies of individuals referred to the NCI Viral Epidemiology Branch (VEB). Referrals are generally for unusual types of cancer or related conditions, known, or suspected to be related to viruses. Kaposi's sarcoma in two homosexual men evaluated in 1981 is a classic example. These referral cases provide the basis for pilot studies that generate hypotheses, the development of protocols for formal investigations of promising leads, and help to set priorities for VEB.