We studied the effects of amending soils with different volumes of water or glucose solution on respiration rates measured as CO2 evolution. Basal respiration was not significantly affected by the volume of water amendment, but substrate-induced respiration in static soil solutions was significantly reduced by increasing water contents. Inhibition of substrate-induced respiration was removed by continuously agitating the incubation vessels. Estimates of substrate-induced respiration rates for six soils differed markedly, depending on whether the vessels were stationary or agitated during the incubation. Agitation allowed increased discrimination between substrate-induced respiration rates for the soils, while static incubation only differentiated the soil with the highest substrate-induced respiration rate from the other soils.