The treatment of malaria tropica is becoming difficult because of the increasing drug resistance rates of Plasmodium falciparum against several of the currently available antimalarias. A fixed combination of rifampicin, co-trimoxazole and isoniazid (Cotrifazid^TM, CF) was found to be highly effective for the treatment of malaria tropica. The aim of the present study in Kenya was to scrutinize this finding in a 14-day trial. Patients with malaria tropica were given in an open, double-arm randomized study CF for 5 days, or chloroquine or pyrimethamine/sulphadoxine as the control. Because of an apparently better activity and tolerance of CF, the randomization had to be stopped after the enrollment of 50 patients. A total of 61 patients in both groups (35 of them between 2 months and 6 years of age) were available for final analysis. All 41 patients treated with CF, originally positive in their blood smears, turned negative; in 2 cases blood smear positivity reappeared on day 14. There were 7 failures in the control group, 4 of them a primary one. Four of those failures were turned negative with CF, 2 failed with CF also, and 1 disappeared. The tolerance of CF was excellent even in infants. In our experience, CF is very well suited for the treatment of malaria tropica, also in cases of apparent drug resistance of P. falciparum against other antimalarials, and even in severe cases of the disease.