Oxygen uptake was determined by manometric methods on the microorganisms in a greenhouse potting soil, a bacterial isolate from this soil, and a bacterial isolate from a peach orchard soil, using as carbon sources the systemic fungicide Benlate (Fungicide 1991, 50 percent wettable powder active ingredient) and the active component benomyl (reagent grade methyl l-(butylcarbamoyl)-2-benzimidazolecarbamate). Uptake by the microorganisms in the greenhouse potting soil was higher in systems containing Benlate than in those without the fungicide. A bacterial isolate (Achromobactersp.) from the greenhouse potting soil, showed higher trends in oxygen uptake with autoclaved soil plus Benlate than in soil with benomyl added at the same concentration. Oxygen uptake by a bacterial isolate from a peach orchard soil (Achromobactersp.) was significantly higher in a system with benomyl, inorganic salts, and glucose than in the same system with Benlate, suggesting an additive effect by benomyl. Results with the bacterial isolate from the peach orchard soil where the fungicide and benomyl were added at the 16-hr time indicated that Benlate and benomyl were inhibitory to oxygen uptake once respiration had begun.