The objective of this study was to measure oestradiol, progesterone and endometrial development among Norplant implant users with bleeding complaints. Seventy-six volunteers complaining of prolonged/frequent bleeding were enrolled. Oestradiol, progesterone and endometrial thickness (assessed by vaginal ultrasound) were determined at that visit. Two thirds of the women had low oestradiol (< 50 pg/ml) and all except one had low progesterone concentrations (< 3 ng/ml). A total of 68% had a very thin endometrium (< 3 mm). A subgroup of 21 women were followed twice a week for 8 consecutive weeks. Oestradiol and progesterone concentrations remained low during the continuous bleeding episodes or short bleeding-free intervals (< or = 15 days), yet increased five- to sixfold (253.4 +/- 142.2 pg/ml) in long bleeding-free intervals. Endometrial thickness remained thin irrespective of the differences in bleeding patterns and oestradiol. We conclude that Norplant implant users with bleeding complaints are usually characterized by low oestradiol concentrations, absence of luteal activity and thin endometrium. A good correlation exists with increasing oestradiol concentrations and longer bleeding-free intervals, but this is not manifested by increased endometrial thickness. However, few subjects bleed with relatively high oestradiol concentrations, therefore a better understanding of the intimate disturbances related to endometrial bleeding in users of long-acting progestins is still pending.