One species of venomous seasnake, Hydrophis semperi, is found in Lake Taal, a large freshwater lake in the Philippines. The first series of seasnake bites occurring in freshwater is described. In one small fishing village, there were eight definite bites and one probably attributable death. In three of the eight patients, specific antibodies to Hydrophis venom were demonstrated. In contrast to previous seasnake studies, there was an absence of asymptomatic cases. The possible public health importance of freshwater seasnake bites in the Philippines needs further investigation.