From the matrix of rat liver mitochondria, three GSH transferases were isolated and named Transferase 1, 2.1 and 2.2. Transferases 1 and 2.2 were purified to electrophoretic homogeneity. Transferase 1 contributes up to about 90% of the total mitochondrial GSH-transferring activity. It has a molecular weight of approx. 45 000 and is composed of two subunits of similar size. The isoelectric point is at pH 7.1-7.4. The Km values for GSH and 1-chloro-2,4-dinitrobenzene are 0.3 and 0.7 mmol/l respectively. Transferase 2.2 has the same molecular weight and subunit structure like the Transferase 1 and an isoelectric point at pH 4.8. The apparent Km values for GSH and 1-chloro-2,4-dinitrobenzene are 0.3 mmol/l and 0.4 mmol/l respectively. Transferase 2.1 contributes only 1% of the total mitochondrial GSH-transferring activity. It has high apparent Km values for both GSH and 1-chloro-2,4-dinitrobenzene (5.6 mmol/l and 1.3 mmol/l resp.) and a limited spectrum of substrates.