The aim of this research project was to investigate ways of improving the accuracy of dosimetric measurements in pion radiotherapy. Interest in this area was stimulated by the results of recent experimental work which revealed that materials from which dosimeters in pion radiotherapy are routinely constructed are not tissue equivalent for pi-. Two means of achieving the stated objective were identified: 1. To produce materials which are tissue equivalent for pions, to use in the construction of phantoms and dosimeters. 2. To evaluate correction factors necessary to convert dose recorded under non-tissue equivalent conditions to that for tissue. An attempt was made to produce muscle and bone equivalent phantom materials. The extent to which the materials produced could be considered tissue equivalent was judged by comparing experimentally determined carbon to oxygen (C:O) and nitrogen to oxygen (N:O) pion atomic capture ratios with those for the corresponding tissue type. Negative pion atomic capture ratios were also evaluated for sets of simple organic compounds to aid further development of the theoretical models necessary to determine correction factors.