Measurements of scintillation light output versus α-particle energy are made for single crystals of organic and inorganic substances excited by monoenergetic α-particles. A new method is used to deduce a relation between the differential efficiency dL/dx and the specific energy loss dE/dx, which in the case of calcium fluoride is verified experimentally using thin evaporated layers. The effect of phosphorescent decay is observed by varying the circuit time constant.The intrinsic spread in scintillation pulse magnitude due to the phosphor is studied by inserting neutral filters between phosphor and photomultiplier and by variation in particle energy. Apart from a spread due to surface irregularities sources of spread are observed in diamond probably due to alternation of fluorescent and non-fluorescent crystal domains, and in anthracene, most likely due to knock-on protons near the end of the α-particle track.