We have studied the effect of HRT on breast tenderness in 61 postmenopausal women randomised to oral or transdermal sequential HRT. An untreated reference group of 29 postmenopausal women was studied concurrently. A questionnaire concerning breast tenderness was administered before and after 10, 12 and 24 weeks of treatment (n = 60) and on 3 occasions at 3-month intervals in the reference group (n = 28). In 10 women with frequent tenderness at baseline, HRT resulted in a reduction at 10 weeks (P < 0.05), which was maintained at 24 weeks (P < 0.05). In contrast, 10 women with infrequent tenderness before treatment reported worsening of tenderness at the 10-week visit (P < 0.01 for transdermal, P < 0.05 for oral), which was not significantly different from the baseline thereafter. These 10 women were older (P < 0.05), and further from the menopause (P < 0.05) than the remaining 40 women who did not develop more frequent tenderness. No significant changes occurred in the reference group. HRT may cause transient breast tenderness, especially in older women and those furthest from the menopause. Paradoxically, it may relieve this symptom in women who have breast tenderness prior to treatment. Breast tenderness should not be considered a contraindication to HRT.