Clobetasol propionate, an anti-inflammatory glucocorticosteroid, was detected in an over-the-counter topical drug product with no indication on the label of this compound as an ingredient. The product was formulated as a topical spray, a cream, or a shampoo and labeled to contain zinc pyrithione as the active ingredient. The finding of clobetasol propionate in the pharmaceutical products was shown by comparison to an authenticated standard of clobetasol propionate by retention time on normal-phase and reversed-phase HPLC, UV spectroscopy, LC-MS and LC-MS-MS. A simple method was developed and validated for the assay of clobetasol propionate by isocratic reversed-phase HPLC. Several lots contained clobetasol propionate at therapeutic levels of 0.02-0.06%. Zinc pyrithione formulations from two other manufacturers were free of clobetasol propionate.