After a discussion of methods of high-energy dosimetry, data on linear energy transfer and quality factors of pions, protons, deuterons and alpha particles in water are summarized. These are shown to approximate the values for tissue and are given both for specific particle energies and as averages for complete tracks. The dosimetry of micro-meson fluxes is considered from a theoretical point of view. The response of personnel monitoring equipment to such fluxes is shown to be “fail-safe” for average particle quality factors of 2.9 or less. External proton beams are shown to be extremely hazardous and some data are given on the response of film badges to beams of protons and pions. Typical depth-dose curves are given. They show substantial build-up only in relatively uncontaminated beams of highenergy particles. Activation of machine parts and targets is described briefly.