A tissue processing apparatus comprises a processing chamber (1), a plurality of reagent containers (5), only one of which is illustrated, and a selector valve (2) for sequentially connecting the processing chamber (1) to each of the said reagent containers (5) to transfer fluid between the chamber and such a container. A vacuum/compression pump (6) and a changeover valve system connected to each of the reagent containers (5) and to the processing chamber (1) is operable to promote reagent flow in a required direction between a reagent container (5) and a processing chamber (1) while maintaining a closed circuit for reagent and gas displaced by the pump between the chamber and the container.