Summary. Dietary depletion of zinc was found to result in a 30% decrease in the total body zinc content of experimental rats when compared with control animals. In the depleted animals there was no decrease in the zinc content of hair, skin, heart or three different skeletal muscles although the levels in plasma, liver, bone and testes were significantly reduced. The analysis of tissues from three patients suffering from disturbances of zinc metabolism suggest that man reacts to zinc deficiency in a similar way. These findings indicate that for a simple screening test of zinc status, analysis of the plasma zinc concentration remains the single most useful measurement.