A field trial was undertaken to test the efficacy of halofuginone lactate in the treatment of East Coast fever under farming conditions in Kenya. The drug was administered orally at a dose of 1.2 mg/kg bodyweight and treatment was repeated after 48 hours. Of 293 cases treated 236 (80.5 per cent) recovered and 49 (16.7 per cent) died. Five animals were disposed of by the owners and three became chronically infected. No differences were recorded in recovery rate between uncomplicated cases and cases with concurrent anaplasmosis or babesiosis, nor were there any significant differences in recovery rates between animals of different types. However, zebu cattle (Bos indicus) tended to respond more rapidly to treatment than exotic cattle (Bos taurus). Younger animals had a poorer recovery rate than adults. Early treatments were more successful than those administered late. It was concluded that with early detection and treatment, coupled with efficient tick control, halofuginone lactate is effective in the treatment of clinical East Coast fever under field conditions.