AbstractEvidence is presented in favour of a natural environmental alkylation process as a source of atmospheric vapour‐phase alkyllead. Several species of marine flora have been cultured under laboratory conditions with added doses of inorganic lead, and production of alkyllead, predominantly trimethyllead (Me3Pb+), has been measured. Atmospheric concentrations and ratios of alkyl and inorganic lead at urban, rural and remote sites suggest that differential decay and deposition processes for different species, together with an environmental alkylation source, may explain enhanced ratios of total alkyllead/total lead in maritime air masse