A mercuric iodide (HgI/sub 2/) photodetector has been used to detect light pulses from gamma-ray and alpha-particle interactions in scintillators. The photocurrent response of an HgI/sub 2/ photodetector to light has been measured and found to be favorable for detecting light from most scintillators, which have their maximum emission between 300 and 500 nm. Energy spectra for alpha particles or gamma-rays from combinations of an HgI/sub 2/ photodetector with various scintillators are presented. The energy resolution of the photopeak from annihilation gamma-rays is 19% with a CsI(Tl) crystal and 24% with a BGO crystal. Fabrication of HgI/sub 2/ photodetectors and their optical coupling to a scintillator crystal are described. The advantages of this new solid-state radiation detector compared to the combination of scintillator and PMT, and some proposed applications, are discussed.