[en] When matter is bombarded by protons, inner-shell ionisation of the atoms occurs and characteristic X-rays are emitted. The intensity depends on the cross-section for inner-shell ionisation, the fluorescence yield of the emitting atoms and the thickness of the target. A study is reported of the variation of X-ray intensity with proton energy over the range 200 keV to 3 MeV. The use of proton-induced X-rays for the study of lead, zinc and copper in material of biological origin, mainly human blood and liver tissue, is described. (U.K.)