Monoclonal employed antibodies against to investigate the various myosins have been employed to investigate the muscle fibre types in limb and tongue muscles of the Queensland cane toad Bufomarinus. The results of experiments using immunocytochemical techniques suggest that these antibodies can detect twitch fibres of types 1 - 3 as well as slow-graded fibres of type 4. 5 as established by Smith and' Ovalle (1973) in the limb muscles of Xenopus laevis. Evidence is presented to suggest that twitch fibres may contain more than one type of myosin in a single fibre. In addition, limb muscles showed seasonal variation in immunocytochemical staining patterns which could be explained by synthesis of type 2 myosin in type 1 fibres. In young toads, a difference in immunocytochemical reactivity of fibres compared with mature toads was found, suggesting the possible existence of foetal myosin in type 1 fibres in these animals. In addition to this, there is a progressive increase of type 2 myosin synthesises in type 1 fibres as the young toads mature to adulthood. Immunocytochemical data also suggest that tongue muscle fibres can be classified into types 1-3 as in twitch limb muscles. In the hyoglossus muscle, a population of fibres displays a staining pattern not found in the limb muscles, suggesting the existence of a unique type of myosin in these fibres.