The presence of potential pathogens and lesions in American oysters, Crassostrea virginica (Gmelin, 1791), from coastal estuaries in Rhode Island was studied. Oysters were collected by hand or tongs from three stations in the Pawcatuck River, two stations in Narrow River, three stations in Charlestown Pond, and three stations in Green Hill Pond, during July/August 1991, November 1991, March 1992, and May 1992. Oysters were processed for histologic examination and determination of condition index. MSX, Haplosporidium nelsoni (Haskin, Stauber et Mackin, 1966), was detected in four of 480 oysters (0.8%); Sphenophyra sp., 15 of 480 (3.1%); Bucephalus sp. 16of 480 (3.3%); crustacea, one f 480 (0.4%); and basophilic inclusion bodies (possible mycoplasm-like organisms) 15 of 480 samples (3.2%). Lesions found in the oysters included: kidney concretions (8.8%); necrosis of the digestive diverticula (5.8%); neoplasia of the digestive tract, connective tissue, reproductive tract, or ctenidia (3.8%); hyperplasia of digestive diverticula (0.2%); ulceration of the stomach epithelium (0.4%); cysts in the kidney (0.8%); atrophic adductor muscle (0.6%); and inflammation of the kidney, ctenidia, gastrointestinal tract, or connective tissue (93.1%). Lesions and parasites were found at all stes studied, although MSX was found only in Charlestown Pond. Condition index -- the resultant of 1,000 times the dry weight of the soft tissues divided by the water-weight volume equivalent of the mantle cavity ranged from 26.52 to 197.67. Disease prevalence in oyster from the Pawcatuck River was not different from other sites, but the condition index values were consistently low (below 75 year around). These findings suggest that low condition index may not necessarily correlate with higher disease prevalence.