A phase fluorometer based on a low‐cost and versatile high‐frequency modulated light source and a fast gain‐modulated photomultiplier is described. The apparatus is particularly well‐suited to high‐sensitivity frequency‐domain fluorescence measurements requiring ultraviolet excitation. The system is very compact since it features a directly modulated light source, a miniature photomultiplier tube, and an rf synthesizer on a PC board. Equipped with a suitable fiber optic probe sensor, the device has potential as a portable unit for a wide range of remote sensing applications. The lamp can be modulated at frequencies up to 120 MHz and the phase fluorometer has been tested at up to 70 MHz with a range of fluorescent lifetime standards containing quinine sulfate quenched with sodium chloride. ©1996 American Institute of Physics.