616 patients with early Trypanosoma brucei gambiense trypanosomiasis (no trypanosomes in the cerebrospinal fluid [CSF] and a CSF white cell count [WCC] of 1-5/mm3) were treated with a combination of pentamidine (6 intramuscular [i.m.] injections of 4 mg/kg) and suramin (2 intravenous [i.v.] injections of 20 mg/kg) in Nioki hospital, Zaire, between 1983 and 1992; 46 (7.5%) of them subsequently relapsed. There was no increase in the frequency of treatment failure during this 10 years' period. Relapses were more frequent in children aged 0-17 years (19/163 [11.7%]) than in adults (26/420 [6.2%] (relative risk [RR] = 1.88, 95% confidence interval [CI] 1.07-3.31, P = 0.04). Even within this small range of CSF WCC, the risk of treatment failure increased in parallel with the WCC count and reached 10/36 (27.8%) in patients with a CSF WCC of 5/mm3. Treatment failures were more frequent (5/30 [16.7%]) in a small group of patients treated with a combination of diminazene (3 i.m. injections of 7 mg/kg) and suramin (one i.v. injection of 20 mg/kg) than in the pentamidine/suramin group (RR = 2.23, 95% CI 0.96-5.21, P = 0.08). Our data support the view that central nervous system involvement occurs early in Gambian trypanosomiasis, which in turn raises doubts about the usefulness of adding suramin to pentamidine, as the former drug, which is more expensive than pentamidine and has to be administered intravenously, penetrates poorly into the CSF and may potentially decrease free pentamidine levels in blood and CSF.