Personnel monitoring for alkyl lead and inorganic lead in air was carried out for six weeks on five workers in an alkyl lead manufacturing plant. Lead in air values were compared to biological values for lead in blood, lead in urine, and delta aminoleuvlinic acid in urine. While variations in each of these measurements occurred, there was no correlation between any of these three measurements and lead in air. Measurement of atmospheric exposure to alkyl lead by personnel monitoring does not provide an accurate assessment of the degree of hazard to workers. When such measurements are performed frequently, they can provide information useful in controlling respiratory exposure. Biological monitoring of lead in urine as practiced by the alkyl lead industry remains the best protection against overexposure to organic lead.