Parenteral administration of long-chain triglyceride emulsions has been shown to have deleterious effects on reticuloendothelial system function in animal models. It is unknown whether this interference occurs in humans with clinically relevant doses of intravenous fat. Two studies were done. Eighteen patients were prospectively enrolled for study. Patients received full feeding by continuous total parenteral nutrition (amino acids 1.5 g/kg/day and dextrose 4.5 g/kg/day) with 33.1 kcal/kg/day. Forty-three % of the nonprotein calories were provided as soybean oil emulsion (Travamulsion 20%) and was administered intravenously over 10 hr (0.130 g/kg/hr). Reticuloendothelial system function was determined by measuring the change in the clearance rate of intravenously injected 99mTc-sulfur colloid (TSC) in each patient. In study 1 (n = 10), one day of lipid (10 hr) was infused, with the clearance of 99mTc-sulfur colloid measured before the lipid was infused and then during the last hour of the 10-hr infusion. In study 2 (n = 8), the clearance rates were measured before the lipid emulsion was begun, and then during the last hour of the infusion on the 3rd day. Clearance rates for TSC after 10 hr of lipid infusion in study 1 did not differ (0.27 +/- 1/min to 0.26 +/- 0.1/min, p greater than 0.10). However, after 3 days of lipid infusion (10 hr/day), a statistically significant reduction in TSC was seen (0.46 +/- 0.08/min-0.27 +/- 0.03/min, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)