Serum and cystic fluid levels of CA 125, CA 19.9, carcinoembryonic antigen (CEA), and alpha-fetoprotein (AFP) were assayed in 74 consecutive women of median age 30 years (range 15 to 74 years) undergoing surgery for adnexal cysts of presumed benign nature. Median (range) serum levels of CA 125, CA 19.9, CEA and AFP were 46.5 IU/ml (4.3-406), 28.5 IU/ml (1-96.3), 1.4 ng/ml (0.5-3.5) and 2.4 ng/ml (1-9.9) in 44 endometriotic cysts; 22.5 (4.7-82), 4.9 (1-226),1.3 (0.7-4.8) and 4 (0.5-10.5) in 11 dermoid cysts, 14 (8.6-25.1), 3.2 (1-6), 1 (0.3-2.8) and 3.7 (1.9-6) in 9 mucinous cysts, and 6.9 (0.5-104), 18 (1-132), 0.8 (0.1-1.9) and 2.1(1-5.4) in 10 cases with mixed histotypes. Corresponding cystic fluid levels were 342,864 (1,418-3,404,682), 228,000 (117-2,500,000), 106 (0.5-2,908) and 1.3 (0.4-51) in endometriomas; 843,895 (10,842-1,676,948), 740,039 (77-1,280,000), 470 (61-880) and 2.5 (1-4) in dermoids; 3,485 (27.2-149,804), 9,007 (36.4-153,475), 1,631 (402-11,096) and 1 (0.5-2.5) in mucinous cysts, and 13,068 (5,300-43,767), 412 (1-142,700), 0.8 (0.4-5.3) and 2.3 (1-4) in the mixed histotype group. No significant between group differences were detected in serum marker levels. Patients in the mucinous cyst group had significantly lower CA 125 cystic fluid levels compared with women with endometriomas and dermoids (P<0.05). Fluid aspirate tumor marker measurements did not aid in the differential diagnosis of benign ovarian cysts, mainly due to the extremely wide scattering of values.