We investigated the relationship between air lead levels and blood lead levels in 132 lead-acid battery workers in two plants who were followed for 30 months between 1983 and 1985 with frequent air lead and blood lead determinations. Both plants converted to more modern, expanded-metal battery manufacturing technologies around 1978 with associated reductions in mean air lead exposures from greater than 100 to less than 30 µg/m3. In multiple regression analyses including consideration of job category, seniority, age, ethnicity, gender, and smoking habit as covariates, there was a highly significant association of blood lead in µg/dL with air lead in µg/m3(partial R2=.20, P < .0001) among the 68 workers in plant B but no association (P = .91) in plant A. Restriction of the regression analysis to those 44 workers in plant B with <or=22 years of seniority yielded the most significant air leadblood lead assooiation (partial R2= .36, P < .0001). Among the remaining 24 plant B workers, seniority, but not air lead, had a significant positive association with blood lead. Despite very stable air lead levels over the 30-month study, the 51 workers in plant A with more than 20years' seniority had a mean decline of 0.04 µg/dL in mean blood lead over the study period, whereas the 13 workers in plant A with <or=20 years' seniority had a mean increase of 7.6 µg/dL. These findings suggest that substantially higher exposures to lead-in-air 20 or more years prior may influence significantly the blood lead levels in workers with subsequent much lower exposure. These findings may have substantial social and economic implications should the current blood-lead level that triggers mandatory removal from exposure under the Occupational Safety and Health Administration Lead Standard be lowered.