Objectives.: In patients with a granulosa cell tumor of the ovary, the value of serum inhibin A and B concentrations for the assessment of disease status was investigated. Methods.: In 30 consecutive patients with a stage I-III granulosa cell tumor, inhibin A and B concentrations were measured in pre- and post-treatment serum samples. Clinical data concerning diagnosis, treatment and follow-up of these patients were related to serum inhibin A and B concentrations. Serum samples from 41 premenopausal females with cervical dysplasia served as controls. Results.: In 30 patients, 13 (43%) recurrences were observed during a median follow-up of 10 years (range 1-31 years). Serum inhibin A and B concentrations were elevated in respectively 67% and 89% of the patients at diagnosis, and in 58% and 85% at recurrence. Inhibin A and B concentrations were normal in all controls. Sensitivity of inhibin A testing for the diagnosis of granulosa cell tumor was 67% with a specificity of 100%, compared to 89% and 100% respectively for inhibin B (ns). Elevations in serum inhibin B concentrations predated recurrences by a median of 11 months. None of the patients in remission showed increased concentrations of inhibin A and B. Conclusion.: Inhibin B seems to be the predominant form of inhibin secreted by granulosa cell tumors and appears to reflect disease status more accurately than inhibin A. Measurement of serum inhibin B concentrations may be preferred for the follow-up of granulosa cell tumors.