The antiproliferative effect of alpha-difluoromethylornithine (DFMO) was investigated in a human ovarian cancer cell line (NIH:OVCAR3) both in vitro and in vivo. DFMO at 5 X 10(-5) M, 5 X 10(-4) M and 1 X 10(-3) M concentrations showed growth inhibition of NIH:OVCAR3 cells in culture. Parallel determination of CA 125 in the culture media of these cells show significant decrease in the presence of DFMO compared to controls. Oral administration of DFMO (2% aqueous solution) to nude mice bearing intraperitoneal tumors resulted in a mean survival of 45 days (38-60) versus 25 days (20-35) for control. Both in vitro and in vivo results suggest that DFMO has potential value in the treatment of ovarian carcinoma and should be considered for clinical trials in appropriate cancer patients.