The hepatic uptake, transport and utilization of plasma lysophosphatidylcholine (lysoPC) and its contribution to biliary lipid secretion have been investigated in bile-fistula rats. The animals were given a single intravenous dose of sn-1-[1-14C]palmitoyl-lysoPC, under constant intravenous sodium taurocholate infusion (1 mumol/min), and the fate of the label was followed in blood, bile and liver for up to 3 h. The livers were excised at given time points, extracted and/or homogenized to determine the lipid distribution and subcellular location of radioactivity. LysoPC was rapidly cleared from plasma, though a consistent fraction of the label persisted in plasma over the experimental time-period in the form of either lysoPC or PC. Recovery of radioactivity in the liver varied from 15.6% after 5 min to 19.5% after 3 h. Hepatic lysoPC underwent rapid microsomal acylation to form specific PC molecular species (mainly 16:0-20:4 and, to a lesser extent, 16:0-18:2 and 16:0-16:1). Ultrafiltration, dialysis and gel-chromatographic analyses of cytosolic fractions (post 105,000 X g supernatants) indicated that lysoPC is transported to the site of acylation mostly as a macromolecular aggregate with an approx. Mr of 14,400. Small amounts of radioactivity were secreted into bile over 3 h (20% in the form of lysoPC and the remainder as 16:0-18:2 and 16:0-20:4 PC species). Plasma lysoPC, taken up by the liver, is mostly transported by a cytosolic carrier with a molecular weight close to fatty-acid-binding proteins; it then enters a distinct acylation pathway, selective for some polyunsaturated-PC species and does not contribute significantly to biliary secretion, either directly, or through its products.