The reef building coral Montastrea annularus was exposed continuously to suspensions of oil and gas-well drilling fluids at concentrations of 0.1 ml/liter, 0.01 ml/liter, and 0.001 ml/liter in flowing seawater at the U.S. Naval Stage I platform. After 6 weeks exposure, coral fragments of 30 to 60 cm sq cm surface area were broken off, rinsed in seawater, and extracted in a one-phase chloroform-methanol seawater extract and returned to the laboratory, the lipids were analyzed for their phospholipid content, alkyl fatty acid composition, and neutral lipid triglyceride glycerol. The aqueous phase was analyzed for free amino acid composition. Biochemical evidence of stress was reflected in the cessation of growth as measured in depressed diacyl phospholipid. Detailed analysis of the acyl fatty acid composition by capillary gas chromatography showed changes in polyenoic fatty acids, suggesting possible changes in the metabolism of the fatty acids induced by the exposure to the drilling fluids.