Glycogen phosphorylase activity was measured in extracts from muscles isolated from a number of body fragments of Ascaris suum females. The highest total activity of the enzyme was recorded in muscles located near the vulva, whereas the lowest activity was found in those from the head and the tail region. No statistically significant differences in the enzyme activity were found between muscles from dorsal and ventral body fragments. The activity of phosphorylase a predominated in muscles from the tail region, whereas that of phosphorylase b predominated in the remaining fragment of the nematode body. The distribution of maxima and minima of total muscle phosphorylase activity along the body of A. suum was opposite to these of alpha-amylase, thus supporting the view on mutual competition between the glycogenolytic and the amylolytic pathway of glycogen degradation.