Thirty-six women with dyskaryotic cervical smears and unsatisfactory colposcopy were randomly allocated to receive either 30 micrograms ethinyl oestradiol or placebo daily by mouth for 10 days. Thirty-four women were available for review (17 women in each of the two groups), full colposcopic inspection of the transformation zone was possible in a significantly greater proportion of the oestrogen treated group (70% versus 23%, P less than 0.01). As most diagnostic conizations are currently performed on the basis of unsatisfactory colposcopy, the use of oestrogen medication followed by colposcopic reassessment should permit a reduction in the number of patients subject to operation.