AbstractOxygen uptake was studied in cell suspensions ofSerratia marcescensBIZIO supplied with various types of substrates. Of the polyols provided as substrates glycerol was the best stimulant of oxygen uptake followed by D‐mannitol and sorbitol. D‐xylitol andmeso‐inositol stimulated oxygen uptake only after a long lag. The hexose sugars as well as their phosphorylated derivatives were better than the pentoses as stimulants of oxygen uptake. Ammonium accelerated oxygen uptake in the presence of fructose, glucose or mannitol. Oxygen uptake in the presence of either glucose‐l‐phosphate or glucose‐6‐phosphate was independent of NADP+, indicating a non