Three methods of switching photomultipliers (pulsing of the first dynodes, pulsing of the whole chain, pulsing of the last dynodes) have been tested and compared on the grounds of a good on/off ratio, a low electrical noise, and a short risetime of the gain. In this work we report the measurements and the results of this research and we find that for our needs the best one is the last for which we obtained an on/off ratio of about 300, a risetime of 20 nsec, and a very low electrical noise.