Serum concentrations of CA 125 and the aminoterminal propeptide of type III procollagen (PIIINP) were measured in 50 patients with clinical stage I or II (N = 16) and stage III or IV (N = 34) ovarian carcinoma before and during cytotoxic chemotherapy. Initially pathological concentrations of CA 125 were found in 92% of all patients and 100% of those in clinical stages II, III and IV. The concentration of PIIINP was at pathological levels in 71% of patients. Serum concentrations of CA 125 (P = 0.04) and PIIINP (P = 0.005) were higher in stages III and IV than in stages I and II. Initial concentration of PIIINP, but not of CA 125, was significantly (P less than or equal to 0.001) higher in the 19 patients who died of the malignancy than in the 31 patients alive at the end of the follow-up period. There was a significant inverse correlation (P = 0.01) between the initial PIIINP values and the survival time among patients with a poor prognosis. Initial concentration of CA 125 was of no prognostic value. During the follow-up, the serum concentrations of CA 125 and PIIINP correlated closely with clinical changes in the disease. Either or both of the tumour markers increased or remained at pathological levels before clinical relapse in patients who had initially responded. PIIINP was a more accurate marker (84%) than CA 125 (63%) in this respect. The information obtained from CA 125 and PIIINP concentrations was identical in 65% and complementary in 33% of the patients.(ABSTRACT TRUNCATED AT 250 WORDS)