The distribution of zinc-tolerant bacteria in sediments from three stream sites containing high (3125 sg g -1 ), medium (291 µg g -1 ), and low (109 µg g -1 ) concentrations of Zn was determined . Zinc tolerance was estimated by the ability of bacteria to grow on media amended with Zn concentrations ranging from 4 to 512 mg 1 -1 . The presence of Zn-tolerant bacteria was correlated with the degree of heavy metal contamination ; this correlation' was more closely associated with readily extractable heavy metal concentrations than with the more rigorously extracted heavy metals . Low concentrations of Zn in media (4 to 16 mg 1 -1 ) were stimulatory to growth of bacteria from contaminated sites while concentrations as low as 4 mg 1 -1 were inhibitory to bacteria from the control site.