The purpose of this study was to determine the measured size distribution of lead (7439921) aerosol in two industries recognized for significant airborne lead concentrations in operations. Operational processes of a brass foundry and a battery manufacturing facility were studied. Sampling was performed via Marple Sierra 290 series (series 294, 296, 298) personal cascade impactors worn by workers during their normal operations. An attempt was made to determine whether a relationship existed between the air lead concentration and the mass fraction of particles greater than 1 micrometer, and also provide estimates of the inhalable, thoracic and respirable fractions of lead aerosol based on the lead aerosol particle size. The size distribution of lead particulate was dependent on the specific type of worker activity that generated the aerosol because various operations exposed workers to lead aerosols of different size distributions. The operations samples were divided into two groups: workers involved in mechanical processes including grinding, cutting, grid casting, pasting, cast on strap unloading, and high voltage welding all of which had lead exposures predominantly consisting of particles larger than 10 micrometers; and, workers involved in mixed activities such as pouring and furnace operations who had variable lead exposures to particles within two or three size ranges. Weak correlations were established between logarithmical transformed airborne lead concentrations and mass percentage of particles larger than 1 micron. The correlations found were either positive or negative, depending on the operation. The authors conclude that their results do not support the generalized assumption, Assumption-C, adopted in the 1978 Occupational Safety and Health Administration's lead standard which assumes that the first 12.5 micrograms/cubic meter of lead in air of lead battery factories is generally composed of small particles, but that as air lead concentrations rise beyond that minimal level, all additional air lead is present in large particles.