31P NMR was used to characterize phosphate pools in perchloric acid extracts of muscles with various composition of muscle fibre types. 2. The white m. pectoralis major (MPM) of chickens 15 min post mortem is characterized by 1.6-times higher relative content of phosphocreatine (PCr) in comparison with mixed leg muscle (LM) of this species. The glycerophosphorylcholine (GPC) does not occur in MPM at NMR detectable level in contrast to the leg muscles. Relative amounts of other phosphates are similar in both muscles. 3. The intermediate MPM of pigeons as well as mixed LM of this species contain 15 min post mortem a very small amount of PCr and ATP but a large amount of inorganic phosphate. Relative content of GPC is higher in leg muscles than in intermediate MPM. 4. Muscles with higher occurrence of white fibres contain relatively more PCr than muscles with lower occurrence of white fibres. 5. The occurrence of GPC seems to be connected with metabolism of red muscle fibres.
