Red and white avian skeletal muscles (chicken and pigeon) contain the same alpha'-isoenzyme of phosphorylase kinase. According to data from gradient polyacrylamide slab electrophoresis in the presence of SDS, the molecular masses of beta- and gamma-subunits of phosphorylase kinase from rabbit, chicken and pigeon muscles are not identical. Electron microscopy data suggest that the quaternary structure of chicken and pigeon phosphorylase kinase is of the same type. The alpha'-isozyme of chicken and pigeon phosphorylase kinase is strongly activated by calmodulin and troponin C. Avian phosphorylase kinase is activated 2--3-fold by phosphorylation with cAMP-dependent protein kinase and by autophosphorylation. This activation is associated with the phosphorylation of both alpha'- and beta-subunits. The affinity of pigeon phosphorylase kinase a for Ca2+ is 20 times as high as that of phosphorylase kinase b.