The occurrence of microorganisms and their relationships with total and available heavy metal concentrations (Cu, Zn, Pb, Cr, Ni, Cd, Hg, and As), as well as main soil chemical characteristics (pH, P, K, Ca, N_tot, C_org) were evaluated in naturally metalliferous serpentine soils and non-serpentine soils with elevated Ni and Cr concentrations. Significant negative correlations were detected between ammonifiers (r = -0.545, r = -0.371), oligonitrofiles (r = -0.478, r = -0.458), total number of microorganisms (r = -0.363, r = -0.393), and available Ni and Cr. The number of actynomicetes and Azotobacter spp. was not affected by heavy metal concentrations, nor any other soil chemical characteristic. Ammonifiers correlated positively with P and K soil content, but negatively with soil C_org. High positive correlations were obtained for available metal concentrations and soil C_org and N_tot, while soil pH only correlated with available Cr and As. Stepwise multiple regression analyses indicated that increased Ni and Cr concentrations had overall little influence on microbial groups, and only ammonifiers were significantly affected by increased available Ni, but P content had an even higher effect on their number in soil.