To identify kidney glutathione S-transferase (GST) isoenzyme, which does not bind to glutathione affinity column, biochemical characterization was performed by using an array of substrates and by measuring sensitivity to inhibitors. Immunological characterization was done by immunoblotting. Affinity flow-through GST exhibited activity towards 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and cumene hydroperoxide, typical class alpha substrates and high sensitivity towards hematin, an alpha class inhibitor. It cross-reacted with antibodies against alpha class GST. Affinity flow-through GST in human kidney is an alpha class member.