Method for the operation of a laser scanning microscope. The microscope includes an illumination beam path in which at least one illumination light source is arranged, a detection beam path in which at least one photomultiplier (PMT) is incorporated as detector, and a control unit for controlling fluorescence experiments. A sample is alternately illuminated at high intensity via the control unit, and the fluorescence decay behavior of sample points and/or sample regions is subsequently detected. The PMT is switched on and off depending on the illumination mode by the control unit via a switch directly in the high-voltage supply of the PMT.