Hematopoietic Neoplasia (HN) has been a significant cause of disease and death in the northern quahog (=hard clam) (Mercenaria mercenaria ) in Wellfleet, Massachusetts (MA). Since the disease was first detected, it has continued to increase in severity and occurrence in aquaculture leases and has decreased the profitability of cultured hard clams . Research by others has determined that a similar disease in Mya arenaria (soft shell clam) and in species of cockles is spread directly between members of those species by a neoplastic cell that enters the water column, infects a naïve animal, proliferates in the vascular system of the infected bivalve and eventually causes its death . A similar scenario appears to be occurring in HN infections of hard clams. Data from recent field research and annual monitoring of hard clams in Wellfleet will be presented confirming that hard clams from different parentages and from different hatcheries are vulnerable to the infectious, tumorous disease. Findings also show that possible resistance to the disease may be present in a subset of hard clams. These survivors could potentially be used to develop resistant hard clam lines.