The status of plasma taurine and whether its concentration can be influenced by total parenteral nutrition (TPN) was determined in 51 malnourished fasting cancer patients after surgery and 7-14 days after starting TPN providing 41 +/- 2 kcal, 0.30 +/- 0.02 g N kg-1.day-1 and 40 mg pyridoxine. Plasma taurine was 50% lower in patients than in control subjects. Plasma taurine was significantly greater than baseline only after 14 days of TPN. We also studied the effects of surgery and taurine supplementation (8.6 mg.kg-1.day-1) on plasma and urine taurine concentrations in 12 malnourished patients. Preoperatively, all patients had normal plasma taurine concentrations; postoperatively, it was in the deficient range in 4 patients. Taurine-supplemented patients initially had higher than baseline concentrations; by day 10, none had subnormal levels. Subnormal taurine concentrations commonly occur in malnourished postoperative cancer patients; surgery further precipitates their fall. Plasma concentrations were maintained only with taurine-supplemented TPN.