Zinc content of serum, hair and erythrocytes, urinary zinc excretion, zinc clearance (CZn) and the ratio of CZn to creatinine clearance (CCr) (CZn/CCr) were measured in 32 children aged between 2.1 and 14.4 years suffering from idiopathic nephrotic syndrome (INS) without renal failure (CCr greater than 70 ml/min 1.73 m2 body surface area). Nineteen subjects had proteinuria and the remaining 13 were in remission. All children received calcium and vitamin D supplementation while on steroid therapy. There was high dietary zinc and protein intake. The results were compared with those obtained from 19 healthy subjects (aged 2-14 years). Zinc concentration in serum, erythrocytes and urine were measured by a colourimetric method. Proton induced X-ray emission was used to determine zinc content in hair. In patients both with and without proteinuria, the mean contents of serum, hair and erythrocytes were significantly lower than in the control group. The urinary zinc excretion, CZn and CZn/CCr in INS children were significantly higher than in the control group. A positive correlation was found between urinary zinc and protein excretion. In spite of high dietary zinc intake and normal intestinal absorption, children with INS had a zinc deficiency. This was probably caused by an increased urinary zinc loss.