BACKGROUND The influence of low doses of aflatoxin B1(AFB1) and partial hepatectomy (PH) on glutathione-S-transferase (GST) activity was studied in the plasma and liver of the rat. METHODS The animals were divided into four groups. The first (I) and the second (II) group were treated with AFB1 freshly dissolved in dimethyl sulphoxide (DMSO), and administered as a single intraperitoneal dose of 50 micrograms/rat 24 hrs after the rats had undergone either sham operation or, 40% PH, respectively. The third group (III) of animals was treated with a total dose of 1 mg AFB1-5 days per week during a period of 8 weeks. The non-treated animals were used as controls (C). RESULTS We observed a significant increase of GST activity in the plasma of all experimental groups compared to the controls (C), (p < 0.02 to p < 0.005). In the liver, the GST activity of all experimental groups was also significantly increased, compared to the controls (from p < 0.02 to p < 0.005). CONCLUSIONS The administration of both single and multiple doses of AFB1 led to long term increase of GST activity in the rat plasma and liver, and partial hepatectomy had no significant effect on this phenomenon.