Hexavalent chromium, which is a mutagen and carcinogen, was efficiently reduced by Streptomyces griseus. This activity was associated with the cell. Cr(6+) reduction by free as well as immobilized cells was studied: cells in PVA-alginate had the highest (100%) Cr(6+) removal efficiency in 24 h with reduction rates similar to free cells. Immobilized cells completely reduced 25 mg Cr(6+) l(-1) in 24 h. PVA-alginate immobilized cells could be reused four times to completely reduce 25 mg Cr(6+) l(-1) in 24 h each time. Chromate in a simulated effluent containing Cu(2+), Mg(2+), Mn(2+) and Zn(2+) was completely reduced by PVA-alginate immobilized cells within 9 h.