Relationship Between Urinary δ -Aminolevulinic Acid Excretion and the Inhibition of Red Cell δ -Aminolevulinate Dehydratase by Lead

83 male workers occupationally exposed to lead and 84 control workers were investigated to find out the degree of delta-aminolevulinic acid dehydratase (ALAD) inhibition by lead which causes a build-up of delta-aminolevulinic acid (ALA) in the body and a resulting increase in its urinary excretion. The critical level was found to be the point at which ALAD activity is reduced to 30 percent of that estimated for a blood lead level of 10 ..mu..g percent, viz, a blood lead level of 45 ..mu..g percent.