The metabolism of platelet-activating factor (PAF; identified as AGEPC: 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and lyso-PAF (lyso-GEPC: 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine) was investigated in cultured rat Kupffer cells. The rat Kupffer cells accumulated [3H]AGEPC and deacetylated this compound to the corresponding [3H]lyso-GEPC, which was the major metabolic product of [3H]AGEPC. [3H]Lyso-GEPC was distributed primarily in the supernatant fraction of incubated cells throughout the experimental interval. Only a very small portion of the [3H]lyso-GEPC was further converted to 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (alkylacyl-GPC), indicating that this acylation process was not particularly active in these cells. When [3H]lyso-GEPC was incubated with Kupffer cells, the conversion of lyso-GEPC to AGEPC via the acetyltransferase reaction increased up to 30 min and declined thereafter. Bovine serum albumin (BSA) had a substantial influence on both the cellular uptake and the metabolism of [3H]AGEPC. An increase in the BSA concentration in the incubation media reduced the cellular uptake of [3H]AGEPC and the subsequent formation of lyso-GEPC. The results of this study suggest that the hepatic Kupffer cells play an important role in the metabolism of PAF. Moreover, these results infer that the regulation of the PAF level in certain hepatic pathophysiological situations may be a consequence of the production and subsequent metabolism of this potent lipid autacoid in the Kupffer cells of the liver.