Investigations were carried out on the ecology of Aedes (Aedimorphus) dentatus (Theo.) in the Ngong Forest near Nairobi between 22 June and 10 September 1971. Five 24-h collections on human bait showed that Ae. dentatus is predominantly a daytime biter with a peak of activity around sunset. At the time of its greatest activity none came to bite on the 7- or 10-m platforms. Of 94 blood-meal specimens, 50 were of Bovid origin (cattle), 18 from unidentified Bovids, 13 from unidentified mammals, one from a bird, three from any primate and nine did not react with the antisera used. Resting adults were frequently found underneath leaves of Hypoestes verticillaris, a herb which grows in partly shaded areas in the forest near the forest edge. A few adults came to bite in a house outside the forest not far from the forest edge. Breeding places were not found. The evidence for Ae. dentatus being a vector of yellow fever is inconclusive. The 33 other species of mosquitoes collected are listed.