The activities of glutathione S-transferase (GST) in rat liver cytosol were investigated sequentially during initiation and promotion of hepatocarcinogenesis by means of the experimental model of Solt and Farber. The results suggested that both diethylnitrosamine and 2 -fluorenylacetamide induced the activity of GST. It was also found that the induced enzymic levels of GST were suppressed by partial hepatectomy and was considered that the suppression of GST was a reasonable phenomenon to hepatocarcinogenesis.