Abstract The development of a specific, sensitive technique for the 24–48 h measurement of tetraalkyl lead (TAL) in air is described. The method, based on that of Hancock and Slater (1975), uses iodine monochloride solution to trap TAL vapour with high efficiency (97–99%). The organic lead is then selectively extracted in the presence of EDTA, to mask any inorganic lead, into a dithizone in carbon tetrachloride solution. Following back-extraction into an aqueous acid solution, lead is determined by flameless atomic absorption spectrometry. The sensitivity of the modified method is of the order of 0.25 ng(Pb) m −3 for a 48 h sample. Concentrations of TAL and inorganic lead measured in ambient air are reported, including the vertical profile above a London street. The method is shown to be suitable for TAL analysis at the low concentrations found in rural air.