A solution to the problem of the flow at low Reynolds number of a dissociated gas about a catalytic probe has been obtained using the method of inner and outer expansions. The solution gives the atom concentration distribution about the probe as a function of the Reynolds number based on diffusion and the parameterK=kw′a/D, wherekw′ is the effective speed of the surface reaction,Dis the diffusion coefficient, andathe radius of the probe. It is shown that, from a measurement of the heat transfer to the probe and an independent measurement of the free stream atom concentration, one can establish the catalytic efficiency of the surface whenK« 1 and the diffusion coefficient whenK» 1. Conversely, knowing either the diffusion coefficient or the catalytic efficiency, the probe may be used to determine atom concentrations. The results of the theory are used to establish experimental conditions in a glow discharge facility under which the sought data may be obtained. Plots of valid operating regimes of this facility are presented as examples.