Loggerhead sea turtles (Caretta caretta) from the Atlantic seaboard (Florida to Massachusetts) were examined at the Marine Pathology Laboratory, University of Rhode Island, from March through December, 1980. Three genera of blood flukes (spirorchids) were found in 14 (33%) of the 43 turtles. Gross signs in heavily infected animals included cachexia, anemia and enteritis. Histopathological lesions were similar to those present in homeotherms with schistosomiasis. Granulomatous gastritis, enteritis, hepatitis, pneumonitis, and nephritis were present. Acute and chronic vasculitis accompanied metastasis of eggs. Infected animals had severe hepatic hemosiderosis, indicative of the anemia observed grossly. Evidence is presented that spirorchidiasis is prevalent in sub-adult loggerhead sea turtles, is responsible for extensive lesions and may be responsible for significant debilitation and mortality.