A method for the determination of hexamethylenetetramine (HMTA) in air as formaldehyde 2,4-dinitrophenylhydrazone is described. HMTA aerosol and gas are sampled on a glass-fibre filter impregnated with phosphoric acid and 2,4-dinitrophenylhydrazine. HMTA is quantitatively converted into formaldehyde and the resulting hydrazone is desorbed from the filter and determined by high-performance liquid chromatography with ultraviolet detection.