Many female Anophelines wander into huts at random, possibly for shelter, and afterwards feed upon any suitable inhabitants.This random wandering can be eliminated by pyrethrum spraying, and the acute discrimination of those Anophelines which enter primarily for food can then be demonstrated.In sprayed huts there was a close relation between the number of men sleeping and the number of Anophelines attracted. The proportions attracted by 3 men and by 1 man were, for A. melas, 2·72; 1: A. gambiae, 2·38; 1: A. funestus, 2·28; 1. Discrimination was reduced at one period by the masking odour of cut and withering bush.There were marked fluctuations in the attractiveness of individuals to Anophelines. On several occasions one or other of the men used as bait suddenly became much more attractive than his fellows, and remained so for several days.The removal of a village increased by only 25–50 per cent. the proportion of mosquitos caught in two huts which were allowed to remain on the village site. This result indicates that most of the mosquitos which had infested the village had been attracted from a distance by the scent, and had not merely arrived in the vicinity of the village by chance.