Genes, especially MHC class II-related genes, expression was examined in porcine-serum (PS)-induced hepatic fibrosis model. Brown-Norway (BN) and Wistar rats were injected intraperitoneally with 0.5 ml sterile porcine serum twice a week for 1, 2, 3, 4, and 8 weeks. Histopathologically, inflammation started at 2 weeks in BN and at 4 weeks in Wistar rats, and hepatic fibrosis developed at 4 weeks in BN rats and at 8 weeks in Wistar rats. Microarray analysis done at 2 and 4 weeks revealed that the expression of MHC class II-related genes and acute phase inflammation-related genes significantly increased at 2 weeks in BN and at 4 weeks in Wistar rats. On the other hand, the expression of some transcription-related genes was down-regulated in both strains. In BN rats, the results of semiquantitative RT-PCR analysis done on four MHC class II-related genes mRNAs corresponded well with those of microarray analysis. MHC class II is considered to be involved in the initiation of PS-induced hepatic fibrosis in rats.