Daily transvaginal ultrasound (US) scanning of the ovaries to assess follicular development and daily blood sampling were performed on 19 Norplant (Leiras, Turku, Finland) subdermal contraceptive implant users who had regular menstrual cycles and on 10 normally cycling women. Three groups were identified in the implant users based on US finding. Six (31.6%) of the implant users had US findings that were consistent with a normal ovulatory pattern. However, their mean peak luteinizing hormone levels and peak midluteal phase progesterone (P) levels were significantly lower than control values. Eleven (57.9%) users had persistent follicles, and 2 users (10.5%) had no follicular development. These data suggest that after 2 to 4 years of use, about one third of Norplant users with regular bleeding patterns may ovulate but most have deficient luteal P levels. In this small study, the presence of persistent follicular enlargement in implant users was common.