Lead has a wide range of applications, and its production and use result in contamination of the environment, including food and drinking water. Geochemical studies indicate that the majority of lead in ecosystems originated from industrial operations, and that human lead intake has increased 100-fold above the "natural" level. Prehistoric human skeletons contain about two orders of magnitude less lead than present-day samples. Biochemical interference with heme biosynthesis can be detected as a result of current lead exposures, inhibition of aminolevulinate dehydratase and accumulation of zinc protoporphyrin in erythrocytes being the earliest effects. Anemia is uncommon except for cases of lead poisoning, but even slightly increased lead absorption results in a decrease in hemoglobin concentrations. Modern neurobehavioral test methods have disclosed increased prevalence of psychological dysfunction associated with augmented lead absorption. Biochemical and behavioral changes occur below the recommended limit for blood lead concentration of 60 micrograms/100 ml. Several diagnostic tests for lead toxicity are available. The protoporphyrin concentration in the blood seems to be the best risk indicator. The highest occupational lead exposures occur in lead smelters and storage battery plants, but several other industrial operations may result in high lead levels. As much as 1% of the working population may have a significantly increased lead absorption with possible adverse effects.