Disseminated neoplasia (DN) is a proliferative cell disorder that occurs in the circulatory system of bivalves. The condition is progressive and lethal. At least 15 species of bivalves over a wide range of geographic locations have been reported to contract DN. Prevalence levels of disseminated neoplasia can reach up to 90% in some populations. In the laboratory, the condition can be transferred to healthy individuals by injection of hemolymph from animals of the same species with high intensity levels of DN. Studies were conducted to investigate transmission of disseminated neoplasia in the soft shell clam, Mya arenaria. It was determined that soft shell clams from two Oregon bays were susceptible to DN by injection, and that the lack of DN in these west coast populations of soft shell clams was not due to disease resistance in these animals. Additionally, it was demonstrated that onset, development of DN, and survival were directly correlated to the number of neoplastic cells injected into the animal. Experiments investigating water-borne transmission showed that the disease is infectious, and an exposure to DN cell in the hemolymph of highly affected clams was sufficient to cause disease. In a cohabitation study, transmission of DN from one DN positive animal to healthy animals was observed, with specific information collected on the length of exposure and DN intensity of the animals involved. Finally, transmission of disseminated neoplasia was not found to be successful using cell-free filtrates prepared from DN cells and DN positive soft shell clam tissue. A PCR enhanced reverse transcriptase assay was employed, and reverse transcriptase activity was detected in samples prepared from DN positive materials. / Graduation date: 1998