Three experiments were conducted on a slightly acidic, grassland clay loam amended with sewage sludge contaminated with Cu, Ni and Zn in different combinations (Cu-Ni, Ni-Zn and Cu-Zn). Metals were added to a low metal sludge at two levels, above and below current limits. The effects of these metals on microbial indices were studied over a 7-week laboratory incubation. Zn inputs had few effects on microbial indices. In contrast, Cu and Ni decreased CO2 evolution at one week of incubation and led to an increase later. Biomass C was lower in high Cu and Ni soils whereas biomass N was lower in all three high metal treatments and there was evidence of a shift from bacterial to fungal biomass. Greater CO2 evolution rates in the high metal soils appeared to be a response to increased stress on microorganisms. Zn seemed to be less toxic than Cu and Ni when applied at rates close to EC limits for sludge treated soil (DoE, 1989).