Growth retardation is seen in experimental animals as a result of severe dietary restriction of several essential trace elements. However, in humans, the effect of zinc deficiency is most pronounced. Growth failure and hypogonadism in males, related to a deficiency of zinc, have been recognized in many developing countries. A mild deficiency of zinc, affecting growth and development in children and adolescents, has been reported from developed countries as well. Zinc deficiency in humans may manifest as severe, moderate, or mild. The manifestations of severe zinc deficiency include bullous pustular dermatitis, alopecia, diarrhea, emotional disorder, weight loss, intercurrent infections due to cell-mediated immune dysfunctions, hypogonadism in males, neurosensory disorders, and problems with healing of ulcers. This condition can be fatal. A moderate level of zinc deficiency has been reported in a variety of conditions. Clinical manifestations include growth retardation and male hypogonadism in adolescence, rough skin, poor appetite, mental lethargy, delayed wound healing, cell-mediated immune dysfunctions, and abnormal neurosensory changes. A mild level of zinc deficiency may manifest with decreased serum testosterone level and oligospermia in males, decreased lean body mass, hyper-ammonemia, neurosensory changes, anergy, decreased serum thymulin activity, and decreased IL-2 activity. Although the clinical aspects of severe and moderate levels of zinc deficiency are well known, the recognition of mild levels of zinc deficiency has been difficult. Currently plasmas zinc appears to be the most widely used parameter for assessment of human zinc status, and it is known to be decreased in cases of severe and moderate deficiency of zinc.(ABSTRACT TRUNCATED AT 250 WORDS)