The combined effect of hormone and cytotoxic therapy on the growth of prostate cancer PC-3 in nude mice was investigated. PC-3 cell was derived from the bone metastasis of a hormone-refractory prostate cancer. Each group consisted of seven animals. After the inoculation of cancer cells, diethylstilbestrol (DES: 20 mg/kg) and futraful with uracil (UFT: 20 mg/kg) were administered for 25 days. DES and UFT synergically inhibited the growth. DES had no effect as a single agent on the growth of a hormone-independent cell line (KM20C) derived from human colon cancer. It also had no additive effect when given with UFT.