A series of 191 endometrial biopsy procedures were performed on Indonesian women who had received between 3 and 12 months exposure to Norplant. In all, 87 biopsy procedures were attempted with a microhysteroscope using biopsy forceps, and 104 procedures were attempted with either Pipelle or Karman suction curettes. Regardless of the biopsy method, diagnosable endometrium was obtained in only approximately 50% of procedures. Myometrium was often found in microhysteroscope but not in suction biopsies. An analysis of a number of clinical characteristics showed that women from whom diagnosable endometrial tissue was obtained had higher mean peripheral oestrogen concentrations in the 2 weeks prior to biopsy (439 +/- 35 versus 289 +/- 33 pmol/l; P = 0.0018) and significantly more days when endometrial bleeding occurred in the 90 days prior to biopsy (26.5 +/- 2.1 versus 16.2 +/- 1.8; P = 0.0003). These results suggest that after 3-12 months exposure to Norplant approximately 50% of women have an endometrium too thin to sample, and that this group is characterized by lower peripheral oestrogen concentrations and reduced menstrual bleeding.