Diary cards of patients in two similar trials of Estrapak-50 hormone replacement therapy were analysed with regard to the characteristics of progestogen-associated bleeding (PAB) and breakthrough bleeding (BTB). Forty out of 52 patients in Study A and 74 out of 92 patients in Study B had diaries suitable for analysis. One patient in Study A and two patients in Study B who withdrew from treatment did so because of unacceptable bleeding problems. Similar results were obtained from both trials. After 6 months of treatment approximately 90% of patients in study A and approximately 70% of patients in study B had PAB on or before day 11. Twenty-seven percent and 49% in studies A and B, respectively, bled prior to day 8, which in the majority of instances affected one treatment cycle. Duration of PAB varied from 1 to 14 days (median 7 days) and the pattern of bleeding in the second cycle was predictive of bleeding in subsequent cycles. Although over 1/3 of women reported some heavy bleeding days, this usually only affected one treatment cycle, and the majority of bleeding was only spotting or light flow. BTB patterns did not raise suspicions of endometrial pathology. Bleeding patterns were both acceptable to patients and, in as much as the current literature indicates that bleeding patterns can be interpreted, were consistent with adequate progestogenic protection of the endometrium.