Expression of the two proto-oncogenes, c-myc and c-fos, in proliferating liver, and the modulation of their expression by 2-mercaptopropionylglycine (MPG) has been investigated. A significant increase in the expression of both c-myc and c-fos was observed, attaining a peak at 30 min, followed by a gradual decline for 8 h after partial hepatectomy. Treatment of partially hepatectomized animals with MPG resulted in a significant decrease in the expression of both genes, the decrease being more marked in c-myc mRNA levels. At later time points, there was a very small rise in the mRNA levels of these genes in MPG-treated animals but they still remained much lower than the peak levels observed in both genes 30 min after surgery. A decline in the recovery of liver weight in MPG-treated animals was also observed. (C) 2002 Elsevier Science Ltd.