EXAMINATION of the literature having shown absence of information on the Joshi effect under radioactive emanations, a detailed investigation was made employing, in the first instance, a β-ray capsule with negligible γ-ray activity. Siemens ozonizer type tubes charged with various vapours and gases and excited by commercial-frequency potentials of kilovolts were used. In agreement with results obtained with visible1 and ultra-violet2 radiation and with X-rays3–6, and employing especially organic vapours, an exposure to β-rays caused an instantaneous and reversible positive effect + Δi at relatively low voltage; with slight increase of voltage, + Δi diminished sharply; and finally changed over to − Δi above Vm, the threshold for a ‘self-maintained’ discharge. Thus, for example, cyclohexane vapour showed under β-rays about 150 per cent positive Joshi effect at 4 kV.; + 9.5 per cent and − 5.8 per cent at 6 and 8 kV. respectively.