A method is described for the specific determination of tetraalkyllead vapour in air. The atmosphere under test is passed through a solution of iodine monochloride in hydrochloric acid, which converts the tetraalkyllead compounds into their dialkyllead ionic forms.A procedure is given in which dialkyllead species are preferentially extracted as dithizonates from the buffered sample solution in the presence of ethylene-diaminetetraacetic acid, which complexes any inorganic lead compounds that may be present. The dialkyllead dithizonates are then decomposed by shaking with a nitric acid-hydrogen peroxide solution and the concentration of lead in the resulting solution is determined by atomic-absorption spectrophotometry, using a carbon furnace for atomisation.The method has a limit of detection of 7 ng of lead in the sample. When expressed as a concentration of tetraalkyllead in air the detection limit is 0·2 µg m–3 for a 10-min sampling period and 0·04 µg m–3 for 1-h sampling period.