Anopheline mosquitoes and their relation to malaria transmission were studied during the months of March, May and July in the Karen village of Mae Tha Waw located in the northwestern mountains of Tak Province. Thirteen species were captured on human bait during 80 man-nights of collecting. Four additional species were collected during routine larval surveys. Anopheles minimus and An. maculatus comprised 92.5% of the specimens captured biting man. Anopheles minimus and An. nivipes were implicated as vectors based on the detection of sporozoite infections using enzyme-linked immunosorbent assays for Plasmodium falciparum and P. vivax. Anopheles dirus was rarely encountered and probably played little part in transmission in Mae Tha Waw during the period of study. Information is provided on nightly biting activity, incidence of disease, infectivity and larval bionomics.