The costs of three types of malaria clinics in Maesot District, north-west Thailand, for a one-year period in 1985-86 were compared from the institutional, community and social (institutional plus community) perspectives. The greatest numbers of patients at the lowest average institutional cost per smear and per positive case diagnosed (US$ .82) were seen at the large central clinic in Maesot town. The peripheral clinic in Popphra, a subdistrict town, had moderate institutional costs per smear and per positive case (US$ 1.58). The periodic mobile clinic, which served five villages on a fixed weekly schedule, had low average institutional costs per smear, but the highest cost per positive case (US$ 3.53). Community costs (those paid by patients and their families) were lowest in the periodic clinic, Addition of a periodic clinic to a system of central and peripheral clinics increased the number of malaria cases treated, particularly those involving women and under-16-year-olds.  Although the periodic clinic entailed a modest increase in institutional costs, it minimized social costs. The results of the study suggest that use a combination of central, peripheral, and periodic clinics, which maximizes access to malaria treatment, minimizes the social costs of malaria.