The gain stabilities and temperature effects were experimentally for three different bias voltage supply modes to photomultipliers at high counting rates. Comparisons of the counting rate effects were made for different bias voltage values and for the anode and the dynode output modes respectively. The factors causing gain variation at high counting rates were discussed. It was shown that the transistor emitter follower supply mode

the lower bias voltage value and the dynode output mode were three effective measures to improve the gain stability at high counting rates.