With 18 communities (9 per group), the study would have 80% power to detect, at the 5% significance level, a 50% decrease in clinical failure rate in eligible children. This number of communities would also permit the detection of a 40% decrease in parasitological failure rate in eligible children with the same power, and at least 60% and 40% increases in clinical and parasitological failure rates, at 5% significance level, in children carrying parasites with CQ resistant genotypes before CQ treatment was started.