We have previously documented the responsiveness of a cell line of human ovarian epithelial carcinoma (Bowman Gray 1) heterotransplanted in nude mice to treatment with the GnRH agonist Lupron-SR. In this study we used another human ovarian epithelial carcinoma cell line, OVCAR-3, and the human endometrial carcinoma cell line HEC-1A. After a latent period, OVCAR-3 tumors showed significant inhibition of growth on Days 17, 21, and 24 (P < 0.03) compared to controls. The effect was transient and did not persist beyond Day 24. HEC-1A tumors showed no inhibition of growth. Radioreceptor assay studies utilizing native radiolabeled GnRH and [D-Lys6]-GnRH revealed no specific GnRH receptors in any of the tumor samples (BG-1, OVCAR-3, HEC-1A, University of Nebraska cell line, and two fresh human ovarian epithelial tumor samples) compared to male rat anterior pituitary cells. Binding studies and the latency and transience of effect would suggest that the mechanism of action in this animal model may be indirect. This activity may be via altered circulating steroids, gonadotropins, cell-cycle regulatory events, or some other as-yet-undefined action related to GnRH agonist administration or indirectly via effects of the metabolic products of degraded GnRH agonist such as D-amino acids, which are incorporated into the cells by constitutive or adsorptive pinocytosis. This study confirms latency and transience of effect of GnRH agonist therapy on an in vivo model of ovarian cancer.