Clostridia are the anaerobic bacteria most frequently associated with foods. They are widely spread in the environment and show an extensive diversity in metabolic activity and nutritional requirements. As they are a rather heterogeneous group, no medium is available which will allow the growth of all clostridia and at the same time exclude the growth of all competitive flora. Most clostridia reduce sulphite to sulphide and hence will produce rather large black haloes of iron sulphide, in iron-containing media under anaerobic conditions. Consequently, most isolation media include sulphite and an appropriate iron salt, so that blackening due to sulphite reduction can serve as a diagnostic test for clostridia. In addition to their diversity in metabolic activity and nutritional requirements, the enumeration of both vegetative cells and clostridial spores using one method is difficult. Many spores only germinate after heat activation, a process which kills the vegetative cells present in the sample. Thus the suitability of a medium depends on the objective of examination, the competitive flora in the sample and the Clostridium species under investigation. The newest media described in the literature are sulphite cycloserine azide medium (SCA) for samples which do not undergo heat treatment before analysis and differential clostridial agar (DCA) for spore counts. Several media for the detection and enumeration of C. perfringens are discussed. Choice will depend on the sample under investigation, the required detection limit and the reason for the test.