Chronic pre- and postnatal exposure of CD rats to low levels of lead resulted in a marked depression in the antibody response to SRBC as well as decreased serum IgG levels. Serum IgM and IgA levels were normal. The fact that the antibody response to LPS, a thymus independent antigen, was not altered, suggested that the T-lymphocyte rather than the B-lymphocyte is affected by lead exposure. Additional significance is lent to these results when blood lead levels in treated rats were found to be similar to levels found in many children in urban areas.