The early diagnosis of lead poisoning -- the most common type of occupational metal poisoning -- based on the determination of the haemprecursors coproporphyrin, delta amino laevulinic acid and free erythrocyte protoporphyrin. Treatment with chelating agents increases urinary lead excretion very effectively. Clinical manifestations of mercury poisoning are different with organic and inorganic mercury compounds. Cadmium poisoning results in inhibition of non-specific enzymes. Depending on the mode of exposure, alteration of the epithelium of the renal tubules or skeletal damage is seen. The toxic effects of chromium are primarily due to direct contact and absorption. Chromium is also carcinogenic. The importance of technical prophylaxis is stressed.