An improved, sensitive method for the determination of formaldehyde in cosmetics and other commercial products is reported. The procedure is based on dilution of the sample with tetrahydrofuran-water (9:1), followed by precolumn derivatization with 2,4-dinitrophenylhydrazine and direct reversed-phase high-performance liquid chromatography. The formaldehyde derivative is stabilized in the reaction medium by addition of phosphate buffer and neutralization and detected in less than 10 min by the standard additions methods. The method also appears to be suitable for the direct evaluation of the formaldehyde donors used in cosmetics as preservatives.