In some areas of endemic trachoma, muscoid flies may play a significant role in transmission of this serious eye infection. A simple and practical method of quantifying the relative household density of synanthropic flies has been developed for use in epidemiological field surveys. The method uses two boards moistened with a 10% sucrose solution. The fly scores showed good reproducibility at the same sampling site during the day and on different days. The only flies identified were Musca sorbens, showing their local density and a significant association of this fly with the presence of inflammatory trachoma in children.