A proportional counter has been designed to detect soft beta‐emitters in the gas phase. Data is presented to illustrate the applicability of the counters to the detection of C14, S35, and H3. Various partial pressures of C14O2have been investigated to determine the effects on the counter properties. Corrections have been made for the counter ends and the memory effects are described. An energy spectrum is presented for H3to determine the low energy limit of the instrument.