The abnormal impactation of a sebaceous follicle (the follicular cast) has been implicated as the preclinical lesion of acne vulgaris. We have characterized the lipid composition of these structures in the first of a series of studies aimed at the identification of sebaceous lipids that may be associated and/or responsible for the initiation of clinical lesions. The lipid composition of follicular casts was analyzed using thin-layer chromatography, gas chromatography, and mass spectrometry. The mean wet weight of the casts was 24.7 +/- 8.6 micrograms and 7.2 +/- 5.6 micrograms (29.4 +/- 13.5%) was lipid. Cholesterol (3.8 +/- 1.8%) and cholesterol esters (2.0 +/- 2.7%), wax esters (25.3 +/- 6.0%), squalene (19.9 +/- 6.6%), triglycerides (16.1 +/- 7.8%), and free fatty acids (33.0 +/- 10.0%) were all present in cast lipid. Fatty acids of the free fatty acid and triglyceride fraction ranged from C12 to C22. The major components of the free fatty acids were C14:0, C15:0, C16:1, C16:0, 2-me-C17:0, and C18:1. In the triglyceride fraction C14:0, C15:0, C16:0, C18:1, and C18:0 dominated. The free fatty acids were composed of normal saturated (50.6%), normal unsaturated (32.8%), and monomethyl branched (16.6%) acids; the triglyceride fraction contained (86.3%) normal saturated (10.8%), normal unsaturated, and (3.0%) monomethyl branched fatty acids. Wax esters of follicular casts included esters ranging from C26:1 to C38:0. Saturated esters predominated and both odd- and even-numbered esters were present. The most abundant fatty acid moieties of these esters were C16:0 and C15:0, whereas C14:0, C17:0, and C20:0 were the most frequently detected alcohol moieties.