The area in which these studies were carried out was the village of Ilobi fifty miles North-West of Lagos. The village clearing, in late secondary forest was half a mile in diameter and had population of fourteen hundred. To the North of the village was farmland, to the East scrub running into late secondary forest and some farmland and to the West a cocoa plantation. The climate in the village was typically hotter and dryer than in the forest. A.aegypti breeding was restricted to the village area and the pre-adults were most abundant in domestic clay water pots, whilst breeding intensity was greater inside than outside the houses. Throughout the year breeding was continuous in the village but in the dryer and hotter months some breeding was observed beyond this area although never within the actual forest. The population fluctuations as indicated by pre-adult numbers were as follows. In the dry season (November to February) the numbers were at a minimum and at the commencement of the rains there was a sharp increase followed by a decline in mid-rainy season (May to July). There was a further increase in August and then a gradual decline toward the end of the year. Laboratory studies indicate some of the factors which control this pattern of breeding and activity. As the adult is almost exclusively anthropophilic the concentration of human population is considered to be a major factor controlling the distribution. The adults show a marked preference for ovipositing in Clearwater as opposed to that which is fouled by organic debris. The breeding intensity inside houses is probably controlled by light intensity and water temperature as adults show a preference for darker and cooler ovipositioning sites.