The efficacy and possible adverse reactions of co-trimoxazole in the treatment of typhoid fever with G-6-PD deficiency were investigated in 68 typhoid children aged 2 to 14 years old. Salmonella typhi was isolated from 45 patients but all had a significant rise of Widal agglutinin titres during the course of the disease. Decrease in G-6-PD activity of the red blood cells was found in 37 out of 51 patients tested. A daily dose of 6--10 mg of trimethoprim plus 30--50 mg of sulfamethoxazole per kg body weight was given for 14 days. Patients with G-6-PD deficiency were closely observed for evidence of intravascular hemolysis. All patients responded well and the mean period of defervescence after starting therapy was approximately 8 days. One patient with G-6-PD deficiency developed acute hemolysis on the second day of medication. The hemolytic symptoms subsided within 14 days with the continuation of co-trimoxazole therapy. No other major side-effect of the drug was observed. It is concluded that co-trimoxazole can be used successfully in the treatment of typhoid fever in G-6-PD deficient children with little risk of serious adverse reaction.