Applies to electro-optical X-ray image intensifiers for medical use, as components of diagnostic X-ray equipment. Describes a method of determining the detective quantum efficiency (DQE) of X-ray image intensifiers by analysis of the single gamma-ray photon scintillation pulse-height spectrum. Themethod applies only to electro-optical X-ray image intensifiers having output radiance decay rates approximately equal to or faster than that of a P-20 phosphor.