A precise method to estimate the cost of malaria in a rural area was developed and applied in 3 villages in Burkina Faso. The estimate takes into account direct costs such as consultation fees, microscopic examinations, medication and transport as well as indirect costs caused by lost work-days. The formula uses 6 variables: age of subject, degree of invalidity, duration of illness, profession, income and percentage of income lost. In the region of Bobo-Dioulasso, 3065 health centre clients were registered in the course of the study: 17% had been clinically diagnosed as having malaria but this was confirmed microscopically in only 11.6% of cases; 73.1% were children aged < 5 years, 13.9% children aged 6-15 years, 12.2% adults aged 16-50 years and 0.8% adults aged > 50 years. Most patients worked in agriculture and trade. The average duration of illness was 4 days, with each case incurring a cost of $11.7 comprised of $8 direct costs and $3.7 indirect costs.