Hexavalent chromium, which is a mutagen and carcinogen, was efficiently reduced by Streptomyces griseus. This activity was associated with the cell. Cr6+ reduction by free as well as immobilized cells was studied: cells in PVA- alginate had the highest ( 100%) Cr6+ removal efficiency in 24 h with reduction rates similar to free cells. Immobilized cells completely reduced 25 mg Cr6+ l(-1) in 24 h. PVA- alginate immobilized cells could be reused four times to completely reduce 25 mg Cr6+ l(-1) in 24 h each time. Chromate in a simulated effluent containing Cu2+, Mg2+, Mn2+ and Zn2+ was completely reduced by PVA- alginate immobilized cells within 9 h.