The guts of 1032 larvae (Ochlerotatus nemorosus, O. rusticus, Culicella morsitans, C. fumipennis, Culex pip-iens, Theobaldia annulata, Anopheles bifurcatus, A. maculipennis) from 8 ponds in Buckinghamshire were examined. Some 90 spp. of algae, common in the larvae, belong for the most part to Chlorophyceae, Diatomeae, and Euglenineae; a few are Heterokontae, Chrysophy-ceae, Cryptophyceae, Dinophyceae, and Cyanophyceae. There is no definite correlation between the number of larvae found and the pH and CO2 content of the water. No definite correlation exists between size of larvae and size of algae eaten. There appears to be no particular preference for any one kind of alga by the larvae, although the spp. of larvae found in a pond seems to be related to the algal flora; e.g., large spp. (Culicella morsitans and C. fumipennis) occur in ponds with larger algal growth. There are apparent correlations between spring and summer phases of algae and the appearance of the larvae. The Culicines eat more algae than the Anophelines, an observation contrary to reports from India. Very few protozoa were found in the gut.