The systemic absorption of copper incorporated into multiload intra-uterine contraceptive devices (IUDs), as indicated by serum copper levels in users of such devices, was assessed in a prospective longitudinal study. One hundred and ten healthy Nigerian women using either multiload copper 250 (MLCU 250) or multiload copper 375 (MLCU 375) IUDs participated in the study. Their serum copper levels were estimated serially during 12 months of continuous use of the devices. The mean (+/- s.e.m.) pre-insertion serum copper levels of our subjects using MLCU 250 (17.0 +/- 3 mumol/l) and MLCU 375 (16.7 +/- 0.5 mumol/l) were found to be lower than those reported in Americans (22.2 mumol/l) and in Germans (20.2 mumol/l), although similar to levels in Indians (17.0 mumol/l). There was no significant difference in the mean serum copper levels estimated before and after 1 month of continuous use of the device. Serial estimations of the serum copper levels in users showed that there was no alteration in these levels after a period of 12 months of continuous IUD use. We therefore conclude that the copper incorporated into multiload IUDs appears not to influence the concentration of serum copper of users.