The time‐resolution capabilities of two 28‐mm‐diam side‐on photomultiplier tubes, Hamamatsu R928 and RCA 931‐A, were studied by point illumination of the photocathode surface with the attenuated beam of a synchronously pumped dye laser (10‐ps pulse width). Using the time‐correlated single photon counting technique, an apparatus response of 112 ps FWHM was obtained. Contour maps giving the time shift and the width of the response were constructed as a function of the point of illumination of the photocathode surface. These data permit selection of the optimized photocathode region to be illuminated during fluorescence decay measurements.