A selective inhibitor technique was used to determine the relative contributions of bacteria and fungi to total microbial respiration in pine forest soils from three "ecologically analagous" sites at intervals of 2.8 km (site 1), 6.0 km (site 2), and 9.6 km (site 3) from a "sour gas" plant emitting sulphur dioxide, SO2. The ratios of bacterial to fungal respiration given as percentages of total activity were 5:95, 14:83, and 18:82 in the F/H horizon and 31:70, 36:62, and 38:62 in the mineral soil (to 5 cm depth) at sites 1, 2, and 3, respectively. An unexplained stimulation of respiration sometimes occurred, however, in the organic soil of site 1, when streptomycin was added. There was a reduction in total microbial biomass in the organic soil of site 1 compared with sites 2 and 3, but no such differences between sites in the mineral soil. The predominant fungi isolated at all three sites wereAureobasidium pullulansfrom intact, washed pine needles andTrichoderma viridefrom washed fragments of the F/H horizon.