Measurements of pre-breakdown currents in hydrogen have been made in uniform fields, in sphere-plane systems and in concentric cylindrical gaps, using the same gas sample. Measurements of Townsend's first ionization coefficient α in the uniform fields were made for E/p (electric field/pressure) between 100 and 1100 V cm⁻¹ Torr⁻¹ and in the pressure range 0·2 to 10 Torr. The multiplication factor exp integral operator α dx was then calculated for the sphere-plane and concentric cylindrical gaps and compared with the measured values. The full current-growth equation for a non-attaching gas was used in each case. The agreement between calculated and measured values in non-uniform fields establishes the validity of the current-growth equation even when the electric field changes markedly over an electron mean free path.