An attempt has been made to study the detailed characteristics of the capture of π^- mesons in light elements, in particular oxygen. This study was made as an initial investigation into the feasibility of the use of π^- mesons in radiation therapy for the treatment of carcinomas. There is a yield of 1.77 ± 0.08 multiply charged particles per π^- capture in oxygen with a mean kinetic energy of 6.9 MeV. These particles have a high relative biological efficiency and low oxygen enhancement ratio so that the biological effect of an irradiation with stopping π^- mesons would be characterized by these heavy particles.The frequency distribution of the various modes of interaction are given together with energy spectra for protons, alpha and heavier particles.