A simple programmed thaw cycle is described, during which the endometrium is prepared with oral oestradiol, followed by a natural progesterone source. This method involves minimal blood tests and uses inexpensive medications. Originally, an i.m. progesterone-in-oil preparation was used. Although highly successful in achieving high serum progesterone concentrations, the daily injections of the oily compound were found to be problematic from the patients' perspective. To examine the possibility of replacing the injectable progesterone with a vaginal preparation we conducted a prospective randomized study of 1 year's duration, during which time 170 and 184 thawing cycles were done with injectable and vaginal progesterone respectively. Although the progesterone blood concentrations obtained with the injectable preparation were more than twice those obtained with the vaginal progesterone, the clinical pregnancy rates (defined as percentage thawing cycles with gestational sac(s)/embryo transfer as demonstrated on ultrasound, 4 weeks after embryo transfer) were similar for both groups (15.9 and 16.8% respectively). Implantation and abortion rates were also comparable. These results agree with previous reports of higher uterine progesterone concentrations after the vaginal application. We conclude that the combination of oral oestradiol and vaginal progesterone is an effective, simple and inexpensive approach for programmed thaw cycles.