This study had been carried out between October 1992 and February 1994 in Koycegiz Lagoon System (KLS) which is a specially protected area (SPA). Residues of organochlorine pesticides (OC) in Callinectes sapidus (blue crab) and in fish (Capoeta capoeta, Oreochromis mossambica, Liza ramada, Chelon labrosus and Anguilla anguilla) from KLS were analysed by gas chromatography. Residues of 5 OC pesticides (alpha-HCH (hexachlorocyclohexane); 0.48 mu g kg(-1), beta-HCH; 0.58 mu g kg(-1), gamma-HCH; 2.60 mu g kg(-1), aldrin; 0.42 mu g kg(-1), and endrin; 1.80 mu g kg(-1)) were found in crab samples, while 7 OC (Total DDT, dieldrin, alpha-HCH, beta-HCH, gamma-HCH, aldrin and endrin) were observed in fish samples. One of them, alpha-HCH was found in all fish species' muscle tissues. The average of results were 6.75 mu g kg(-1) for C. capoeta; 35.90 mu g kg(-1) for O. mossambica; 26.30 mu g kg(-1) for L. ramada; 5.33 mu g kg(-1) for mu g kg(-1) for C. labrosus; 5.00 mu g kg(-1) for A. anguilla.