Anopheline mosquitos and their relation to malaria transmission were studied 3 times: in July and August, 1999; in December, 1999; and in August and September, 2000. The studies took place in the malaria endemic villages of Khammouane Province, southeast of Lao PDR. A total of 28 species were collected using human and animal bait. Human bait attracted predominantly Anopheles dirus and An. minimus, which were identified as vectors by the detection of sporozoites by dissection, PCR, and enzyme-linked immunosorbent assays for Plasmodium falciparum and P. vivax. The vectorial capacity of An. dirus was 0.009-0.428, while that of An. minimus was 0.048-0.186. The inoculation rate of An. dirus was 0.052-0.137 (Boualapha; August, 2000). An. nivipes and its sister species, An. philippinensis, were principally zoophilic, although a considerable number of the females were also attracted to human bait in the villages of the paddy field areas. An. philippinensis infected with oocysts of P. vivax was detected in a specimen collected by animal bait. These two species were considered as vectors in Khammouane Province. Four species, An. notanandai, An. sawadwongporni, An. willmori, and An. hodgkini, had not been recored before in Lao PDR. Information is provided on host preference and the nocturnal biting activities of common species and the incidence of malaria in the study areas.