Serum values of alpha 1-acid glucoprotein (alpha 1-AG) were measured by a radial immunodiffusion technique before the primary operation of 60 ovarian tumors and before the second-look laparotomy of 80 ovarian carcinomas. The results were compared with cancer antigen 125 (CA 125) measurements performed in the same samples by a radioimmunoassay or enzymeimmunoassay. The sensitivity and negative predictive value of the alpha 1-AG measurements were low both before the primary operation (37% and 31%, respectively) and the second-look operation (10% and 51%, respectively). Inversely, the CA 125 measurements before the primary operation demonstrated a sensitivity and negative predictive value of 93% and 81%, respectively. In the second-look group the corresponding CA 125 results were 41% and 62%, respectively. The specificity and positive predictive value of alpha 1-AG before the primary and the second-look operation were high and almost identical to those of CA 125 (93%-100%). All patients with increased alpha 1-AG values also had increased CA 125 levels. Alpha 1-AG cannot be distinguished from immunosuppressive acidic protein (IAP) by radial immunodiffusion technique. In conclusion, the alpha 1-AG analyses did not add new information to the CA 125 measurements. The use of alpha 1-AG (or IAP) as a tumor marker in ovarian cancer cannot be recommended.