The results of biochemical tests used for the supervision of factory workers exposed to lead (notably lead serum levels, urinary aminolevulinic acid (ALA) and punctuated red cells) were compared in 90 patients. The reference test used to evaluate the sensitivity and specificity of these examinations was EDTA-induced lead urinary excretion. Lead serum levels and urinary ALA were about equally effective in providing information. However, these two tests were more sensitive when performed simultaneously than when performed separately. It is suggested that both should be requested when trying to prevent lead poisoning.