The aim of these experiments was to investigate the expression of cyclin D1 and of oestradiol receptors as well as the level of [(3)H]oestradiol binding in leiomyoma and adjacent myometrium from human uteri at different menstrual phases and at an early stage of menopause. [(3)H]oestradiol binding was determined by saturation analysis, while the oestradiol receptor (ER) alpha and beta and cyclin D1 levels were determined by Western blot analysis of 16 samples of human leiomyomas and corresponding myometria at different hormonal stages. In leiomyomas during all phases of the menstrual cycle, ERalpha expression, high affinity oestradiol binding and cyclin D1 expression were all elevated in comparison with adjacent myometrium. ERbeta expression and low affinity oestradiol binding were enhanced in leiomyomas only during the proliferative phase. During menopause, ERbeta expression and low affinity binding were enhanced in leiomyomas, while the ERalpha expression was not significantly enhanced and cyclin D1 levels were similar to that in myometrium. Only the oestradiol binding exhibited any menstrual cycle-related changes. Our data suggest the involvement of cyclin D1 in the growth of leiomyomas during the menstrual cycle. In menopause, there appears to be a switch from ERalpha to ERbeta expression in leiomyomas, and the induction of cyclin D1 is decreased. The regression of tumour may ensue from these changes at menopause.