Five patients with advanced ovarian granulosa cell malignancies resistant to cytotoxic chemotherapy were treated with monthly subcutaneous injections of long-acting gonadotropin releasing hormone (GnRH) agonist analog. One partial response and one stabilization of the disease were observed. In three patients, the tumor continued to progress. Treatment response was monitored with serum inhibin assay. Four patients had high serum inhibin concentrations at the beginning of GnRH analog treatment, while one patient had an inhibin-negative tumor. In three of four patients, serum inhibin remained relatively constant, or decreased during the first 3 months of therapy. It subsequently increased, in parallel with clinical deterioration. Further clinical trials with GnRH analogs are warranted in this malignancy in which serum inhibin appeared to be a clinically valuable tumor marker.