1. Balances of twenty trace elements (silver, arsenic, gold, bromine, cadmium, cobalt, chromium, caesium, copper, iron, mercury, lanthanum, molybdenum, rubidium, antimony, scandium, selenium, samarium, tungsten and zinc) have been determined in four male patients during total parenteral nutrition incliding fat emulsion and a special solution for addition of Fe, Zn, manganese, Cu, fluorine and iodine, besides calcium and magnesium, to the infusion solutions. 2. The analyses for trace elements were made with the aid of an ion-exchange technique based on neutron activation, and combined with subsequent gamma spectrometry. 3. The intended intravenous supply of trace elements correspond approximately to the analysed supply. However, all the other trace elements determined were found to be unintentionally administered in small amounts. 4. There was a substantial retention of Fe. Other elements retained were Ag, Co, Cr, Cu, Sb, Sc, and W. 5. Particularly Br and Rb were lost by the patients, but negative balances were also found for As, Au, Cd, Cs, Mo, Se and Zn. However, Zn was retained by one patient with short bowel syndrome. 6. The serum concentrations of thirteen (Ag, Br, Co, Cs, Cu, Fe, Hg, Mo, Rb, Sc, Se, W and Zn) of the trace elements were found to have some decrease during the period of total parenteral nutrition, mostly in accordance with the corresponding balance values, Fe, in particular, was found to have the derectional change in concentration. 7. The administration of trace elements is recommended in long-term total parenteral nutrition.