There have been few published data on immunological effects of lead in man. In this report, blood lead concentration, lymphocyte count, T-cell and B-cell lymphocyte subpopulation and absolute count, peripheral eosinophil count and PHA induced in vitro blastoid transformation were studied in 35 lead smelters and 11 control workers. T-cell subpopulation was significantly lower and B-cell subpopulation as well as B-cell absolute count were significantly higher in lead workers compared to the control workers. On the other hand, no statistically significant differences were found in T-cell absolute count and PHA induced blastoid transformation. Consequently, it was concluded that any quantitative or qualitative change may not be induced in T-cell lymphocytes at the observed level of lead exposure and it was suggested that the humoral immunity of lead workers was influenced by apparent increase of B-cell lymphocyte count in lead workers. The dose-effect relationship between blood lead concentration and the increase in B-cell lymphocyte count could not be ascertained due to the lack of data at intermediate levels of lead exposure.