Lead exposure causes cognitive and behavioral deficits in some children. We have proposed that the effects of single nucleotide polymorphisms (SNP) of the human pseudodeficient arylsulfatase A (ARSA) gene that result in reduced levels of the enzyme, and lead concentrations that decrease ARSA activity, culminate in cellular enzymic activity that is below a critical threshold required for the normal nervous system function. Human fibroblasts grown in the presence of lead acetate exhibit a 65% decrease in ARSA protein, resulting in a significant decrease in the ability to catabolize sulfatide in cells from individuals with the SNP(s) of pseudodeficient ARSA, but not those from subjects with the normal gene (Poretz et al., Neurotoxicology 21 (2000) 379). The present study examines the potential of lead to affect the biosynthesis, trafficking and turnover of ARSA in human fibroblasts. Fibroblasts, grown in 20 microM lead, displayed a 44--58% increase in the rate of proliferation. Lead caused a decrease of approximately 33% in the accumulation of newly synthesized intracellular ARSA. This difference was not due to increased rates of intracellular degradation of ARSA or decreased levels of ARSA mRNA. Lead, however, caused the newly synthesized enzyme to be trafficked through the secretion pathway, resulting in decreased amounts of the enzyme in intracellular compartments. Though lead exposure results in increased cellular proliferation, it appears to cause decreased intracellular steady-state levels of ARSA by affecting the sorting cues and/or mechanisms directing the enzyme to lysosomes.