In order to accurately determine sex hormone dependency and hormone responsiveness in human esophageal carcinoma, the effects of sex hormones on the growth of esophageal carcinoma cell lines, KSE-1 and KSE-2 cells, were examined in vitro and in vivo. Cell proliferation of cultured KSE-1 cells was inhibited by treatment of estradiol and enhanced by dihydrotestosterone (DHT), whereas KSE-2 cells were unaffected by these sex hormones. The heterotransplanted tumors of KSE-1 cells in nude mice possessed estrogen receptor (ER) and androgen receptor (AR), while the tumors of the KSE-2 cells had neither ER nor AR. When the tumor growth rates and serum hormone levels were monitored during the continuous administration of either estradiol or DHT, no significant differences were observed in either the serum hormone levels or tumor growth rates between male and female mice. The administration of estradiol significantly inhibited the growth of ER-positive and AR-positive KSE-1 tumors in both males and females in conjunction with an increase in the estradiol levels and a decrease in the DHT levels in the serum. However, the growth of ER-negative and AR-negative KSE-2 tumors was not influenced by either estradiol or DHT administration. These results suggest that the in vivo growth of human esophageal carcinoma cells with sex hormone receptor is influenced by circulating hormone levels and can be manipulated by systemic estradiol administration.