The most important changes in lipid composition during larval development in the honeybee, Apis mellifera, were noted in the total weight of the fatty acid classes, Palmitic acid and a CIS: I acid, presumably oleic, were the most abundant fatty acids in the different lipid classes during larval development, together accounting for more than 70% of the total. The proportions of the fatty acids changed very little during development. Of the sterols, 24-methylene cholesterol was most abundant in both the free and esterified forms except on the first and second days when cholesterol ester was more abundant. Cholesterol-ester concentration decreased in such a way that on the fifth larval day the percentage composition of the sterol esters was almost identical to that of the free sterols. The composition of the free sterols remained practically constant during development.