[en] Pion, proton and heavy ion beams are used extensively in bio-medical applications, the attraction being the high proportion of heavily ionizing short range secondaries localized at the stopping region, giving rise to a greater dose being deposited at the end of the range. However interactions in flight reduce the advantage either by deflection or absorption and thus the dose measurement is insufficient to model biological effects due to the changing radiation quality. Experimental investigations of such interactions are here reviewed and the experimental data arising examined in respect of input to models for radiobiology and treatment planning. 78 references. (U.K.)