This ongoing prospective longitudinal study involved 23 women who had complete records, of 37 healthy non-breastfeeding informed volunteers recruited from our family planning clinic since August 1997 to the Norplant training programme. Packed cell volume (PCV), white blood cell (WBC) concentration (total and differential and platelet concentration were analysed at pretreatment and at 12, 24 and 36 months' followup. Statistical analysis was with paired t-tests. The level of significance was set at 5%. Each acceptor received a menstrual calendar to document all events of bleeding. The mean PCV was 40.5 +/- 2.4% at pretreatment. This rose to a statistically significant (P < 0.001) mean value of 44.9 +/- 4.4% at 36 months. The mean WBC concentration at pretreatment was 5552 +/- 1423 per mm3 which declined statistically (P < 0.001) to a mean value of 4400 +/- 1281 per mm3 at 12 months without any further significant changes at 24 months (P > 0.6; 4143 +/- 1301 per mm3 and at 36 months (P > 0.9; 4070 +/- 875 per mm3). At 24 months of study the mean concentration of neutrophils, lymphocytes, monocytes eosinophils and basophils did not change significantly from their respective mean concentrations at 12 months. These insignificant changes were also manifested at 36 months of study in the lymphocytes (P > 0.2), eosinophils (P > 0.5) and basophils (P > 0.2), even though there was a significant decrease in the neutrophils (P < 0.05) with a corresponding significant increase (P < 0.001) in the monocyte concentration. However, there was still a significant decrease (P < 0.001) in the WBC at 36 months of study compared with the mean preinsertion value, which was manifested mainly in the neutrophil concentration (1403 +/- 517 per mm3 (P < 0.001). The mean value of platelet count (136260 +/- 27664 per mm3) at 24 months showed no significant change compared with the 12 months value (126174 +/- 37977 per mm3). The value at 36 months (125391 +/- 18858 per mm3), however, still showed a significant decline over the pretreatment mean concentration (208043 +/- 27250 per mm3). None of the acceptors had thrombocytopenia at 24 and 36 months. At 2 years and 3 years of studies 60.9% and 47.8% of Norplant users reported irregular bleeding patterns, mainly of reduced episodes. The continuation rate at 36 months was 100%. Women using the Norplant implant are at an advantage, because in spite of the variable aberrations in their menstrual pattern, the packed cell volume increased. The changes ob-served in the white cell and the platelet concentrations did not lead to adverse effects.