Mixed, washed cell suspensions of denitrifying bacteria were unaffected with regard to the rate of denitrification by increased surface areas in the form of glass beads, clays, and oven-heated soils of different textures. Evolution of the soluble gases, nitrous oxide and carbon dioxide, was increased with increased surface area. Formation of gaseous nitrogen from cells incubated in an argon atmosphere always exhibited a characteristic lag period. This lag period was attributed to the solution not being saturated with nitrous oxide since the lag was abolished when cells were incubated in a nitrous oxide atmosphere.