Eight normal children and eight patients with inborn errors of metabolism have had balance studies performed for the following elements: nitrogen, phosphorus, potassium, sodium, calcium,magnesium, iron, manganese, zinc, copper, molybdenum, cobalt, chromium, nickel, cadmium, stronium, and lead. In six of the patients natural protein was largely replaced by amino acids (Aminogran: Allen & Hanbury Ltd., and MSUD aid: Scientific Hospital Supplies Ltd). Depending upon age they were allowed a variety of other foods such as fruit and vegetables which contain minerals and trace metals. A mineral mixture was provided to augment the trace metal and mineral intake from these allowed food items with the aim of making the total intake comparable with that of healthy children on a free diet. This mixture was shown to be deficient in zinc and manganese. In addition results of the balance studies showed that although the dietary intakes of iron and copper from the synthetic diets were comparable with those of healthy children, the patients retained significantly less of these metals. Appropriate increases of all four metals in the mineral mixture are therefore recommended. A further two patients received an acid hydrolysate of casein (Minafen: Trufood Ltd.) instead of most of the natural protein in the diet. Balance studies indicated that the content of minerals and trace elements was satisfactory. A new mineral and trace metal mixture has been formulated from the intakes of the healthy children. This mixture is sufficient to provide patients receiving synthetic diets in which few or no additional foods are allowed, with adequate amounts of all the essential minerals and trace metals. Iodine, an essential non-metallic element, was not included in this study.