Recent results from our laboratory indicate that muscles obtained at 3 min postmortem from stress susceptible (SS) pigs have slightly higher levels of cyclic AMP (c-AMP) than muscles from control (C) pigs. Since c-AMP affects glycogenolysis and an abnormality of this process is a characteristic of SS pigs, this research was conducted to determine whether the elevation in c-AMP level is due to an increase in the rate of synthesis or to a decrease in the rate of c-AMP degradation. Specific activities of adenylate cyclase, the synthetic enzyme, were 146 f 62 (SD) for SS and 168 ± 46 pmoles/min/mg protein for-C; this difference was not significant (P = 0.05). Specific activities of cyclic 3′,5′-nucleo-tide phosphodiesterase, the degradative enzyme, were 403 ± 58 for SS and 415 ± 66 pmoles/min/mg protein for C; this difference was not significant (P = 0.05).