The proportions of the major lipid classes extracted from the cuticle of the black carpet beetle, Attagenus megatoma, remained relatively constant throughout the larval period (about 260 days) but differed considerably from those in the surface lipids of the adult. Wax esters made up about 60% of the cuticular lipids in the larvae but only 12% in the adults. Hydrocarbons constituted 15–20% of the larval cuticular lipids but became the major lipid class (55%) in the adults. The composition of the hydrocarbon fraction of the adults differed qualitatively and quantitatively from that of the larvae. A homologous series of five alkenes was identified in the adults by using gas chromatography-mass spectrometry. One of these, 9-pentacosene, was the predominant component (31%) of the adult hydrocarbon fraction. Internally- and terminally-branched alkanes were also identified but they made up only about 2% of the total hydrocarbon fraction of the adults. The proportion of free fatty acids was similar in the larvae and the adults, but an increase in the amount of unsaturated fatty acids occurred in the adult stage. These total results indicate a shift from an abrasion-resistant hard wax layer in the larvae to a softer cuticular wax in the adults.