Eighty-five consecutive general hospital patients requiring total parenteral nutrition (TPN) were prospectively studied in order to evaluate the safety and efficacy of a '3-in-1' nutrient mixture. All formulas were individualized to estimated requirements (average composition nitrogen 14 g, glucose 350 g, fat 50 g), mixed in the hospital pharmacy, contained within 3-litre EVA plastic bags, and given to the patients as a continuous 24-hour infusion. The average duration of TPN was 19 days per patient (range 8 - 84 days). Judging by nitrogen balance and plasma protein concentrations, the system was effective in maintaining or improving nutritional status in patients in a relatively stable condition but not in those who were critically ill (e.g. those in an intensive care unit). Development of magnesium and iron deficiencies was common during the period of TPN (25% of patients developing magnesium deficiency and 40% developing iron deficiency) despite daily supplementation with commercial trace element mixtures, but these states were easily corrected by high-dose administration. 'Creaming' of less than 5 mm on the surface of the emulsion was common, whereas that of more than 10 mm was rare (12 bags) and invariably associated with excessive addition of polyvalent cation or glucose. Deposition of lipid on the internal surface of the catheter was a common problem after 2 weeks' continuous administration. Temporary problems with faulty bag connections resulted in excessive catheter sepsis (14%) due to Staphylococcus epidermidis. Mild reversible disturbances in liver function occurred in one-third of the patients. The system appears safe and effective for the management of most patients requiring long-term TPN.(ABSTRACT TRUNCATED AT 250 WORDS)