The metabolism of succinate was examined in the housefly Musca domestica L. The labeled carbons from [2,3-14C]succinate were readily incorporated into cuticular hydrocarbon and internal lipid, whereas radioactivity from [1,4-14C]succinate was not incorporated into either fraction. Examination of the incorporation of [2,3-14C]succinate, [l-14C]acetate, and [U-14C]proline into hydrocarbon by radio-gas-liquid chromatography showed that each substrate gave a similar labeling pattern, which suggested that succinate and proline were converted to acetyl-CoA prior to incorporation into hydrocarbons. Carbon-I3 nuclear magnetic resonance showed that the labeled carbons from [2,3-13C]succinate enriched carbons 1,2, and 3 of hydrocarbons with carboncarbon coupling showing that carbons 2 and 3 of succinate were incorporated as an intact unit. Radio-high-performance liquid chromatographic analysis of [2,3-14C]succinate metabolism by mitochondria1 preparations showed that in addition to labeling fumarate, malate, and citrate, considerable radioactivity was also present in the acetate fraction. The data show that succinate was not converted to methylmalonate and did not label hydrocarbon via a methylmalonyl derivative. Malic enzyme was assayed in sonicated mitochondria prepared from the abdomens and thoraces of 1-and 4-day-old insects; higher activity was obtained with NAD" in mitochondria prepared from thoraces, whereas NADP+ gave higher activity with abdomen preparations. These data document the metabolism of succinate to acetyl-CoA and not to a methylmalonyl unit prior to incorporation into lipid in the housefly and establish the role of the malic enzyme in this process.