A total of 55 non-breastfeeding informed volunteers were recruited into a prospective longitudinal study from a family planning clinic between September and December 2002. Blood samples were collected at pre-treatment and at 3, 6 and 12 months follow-up, for packed cell volume, platelet count, prothrombin and activated partial thromboplastin time. Statistical analysis was with paired t-tests. The level of significance was set at 5%. Each subject received a menstrual calendar to chart all bleeding and spotting events. The mean age and weight of acceptors were 32.5 +/- 6.1 years and 63.6 +/- 9.6 kg, respectively. Mean packed cell volume (PCV) was 35.2 +/- 2.9% at pre-insertion. This rose to significant mean +/- SD values of 36.5 +/- 3.1%; p<0.05, 38.5 +/- 2.8%; p<0.0001 and 38.4 +/- 3.6%; p<0.0001 at 3, 6 and 12 months, respectively when compared with the pre-insertion mean value. The mean values of the platelet count showed no significant change at 3 months (238,448 +/- 68,618 mm(3); p>0.9), compared with pre-treatment value (240,545 +/- 96,769 mm(3)). There was a significant reduction in mean concentration at 6 months (p<0.009; 191,364 +/- 55,531 mm(3)) and at 12 months (p<0.003; 202,773 +/- 81,544 mm(3)) follow-up. The prothrombin and the partial thromboplastin time did not show significant change over their pre-insertion mean values of 12.0 +/- 1.1 s and 36.9 +/- 2.9 s, respectively. At 12 months, 79.5% (35) of the users reported an abnormal menstrual pattern, which included 54.5% (24) reduced bleeding pattern, 20.5% (9) increased bleeding and 4.5% (2) of combination of patterns. Only 20.5% (9) had a normal menstrual pattern. The continuation rate was 98%, as one user discontinued because of headaches. Norplant (the registered trademark of the Population Council for levonorgestrel subdermal implants) had an effect on the bleeding pattern - mainly reduced bleeding. The increase packed cell volume is beneficial in preventing anaemia. There was no detrimental effect as a result of the reduced but normal platelet count and users were not predisposed to clotting abnormalities.