Epidemiological and experimental evidence support a role for sex steroid hormones in colorectal cancer. The aims of this study were to determine expression of oestrogen receptor in adenoma derived and carcinoma derived colonic epithelial cell lines, and to determine the in vitro effect of beta oestradiol on growth. Between 0.5-1.5 fmol/mg protein of oestrogen receptor was expressed in the colonic cell lines studied. mRNA for oestrogen receptor was also expressed. An adenoma derived cell line, AA/C1, demonstrated an increase in growth rate in response to beta oestradiol. The effect was density dependent. The cell line AA/C1/SB10, a chemically transformed derivative of AA/C1, did not respond to beta oestradiol. Adenoma derived and carcinoma derived colonic cell lines express oestrogen receptor. Oestrogen may have a trophic action in vivo on premalignant colonic epithelium.