This disease consists of multicentric, disseminated tumors and is largely restricted to one species of reef fish, the bicolor damselfish (Eupomacentrus partitus). These neoplasms are visible externally as small masses up to several millimeters in diameter and also may be found scattered throughout the body musculature and soft tissues.  The tumors are sometimes invasive and destructive of adjacent bone and soft tissue, and may be capable of metastasis.  Preliminary histological examinations have indicated that these tumors probably originate from the myelin sheaths of peripheral nerves and may therefore be classified as neurilemmomas or schwannomas.  Many factors make these tumors in the bicolor damselfish an ideal and unique model system for the study of the development and epizootiology of spontaneously occurring tumors in a nature animal population.  The highly territorial social system of this species provides a unique opportunity for monitoring diseased and health individuals in their natural habitat over long periods of time (6 months or longer).  The highly conspicuous appearance of the tumors also allows rapid visual censuring of populations to determine prevalence rates of tumored fish on different reefs. Preliminary observations have indicated that prevalence rates on six reefs in South Florida range from 0. 2 to 5. 0%.  The relationship between tumor prevalence rates and fish size, population densities, habitat types, and geographical locations of reefs are presently being investigated and will be discussed.