Culex vishnui group consists of 3 species of mosquitoes vizCulex vishnui, Culex pseudovishnui andCulex tritaeniorhynchus. It was found that out of 16 species of mosquitoes collected in 3 years from two different biotopes, 8·28 and 24·89% ofCulex vishnui mosquitoes were collected from human habitations and cowsheds respectively. The corresponding data ofCulex pseudovishnui were 1·80 and 5·66% respectively. Out of 12274 mosquitoes belonging to 17 species collected off man-baits in one year,Culex vishnui constituted 34·6% while the latter species encountered 9·04%. When the collection was made by placing manbaits and cow-baits side by side, the attraction ratio (man:cow) ofCulex vishnui was found to be 1∶1·9 and that ofCulex pseudovishnui was 1∶2·6. Bloodmeal analysis of these two species of mosquitoes revealed thatCulex vishnui was more inclined to human blood (21·5%) than that ofCulex pseudovishnui (16·14%).Culex vishnui andCulex pseudovishnui were both susceptible to DDT, dieldrin and malathion, but the LT50 value was slightly higher in the former species than the latter.Culex vishnui utilised its breeding spots like paddy fields, ponds, ditches and burrow-pits more effectively in almost all the months of a year thanCulex pseudovishnui. The density of the larvae ofCulex pseudovishnui was found to be lower than that ofCulex vishnui. Japanese encephalitis virus was isolated only fromCulex vishnui in West Bengal.