The control of the attainment of acclimation in Cancer pagurus has been studied. Homologous (8 or 22°C) and heterologous acclimation [central nervous system (CNS) and periphery of crabs simultaneously held at 8 or 22°C] were used. The dependence of electrophysiological parameters of dactylopodite closer muscles of walking legs on nerve stimulation was determined between 6 and 26°C. Muscle resting potential (RP) hyperpolarized linearly with increasing measurement temperatures and showed a 69% compensation between 8 and 22°C on homologous acclimation. With the CNS temperature constant at 8°C, the leg muscle RP showed a 72% compensation on heterologous acclimation to 8 and 22°C; when CNS temperature was constant at 22°C, leg muscle RP showed a 48% compensation on heterologous acclimation to 8 and 22°C. In homologous acclimation, the shape of the excitatory junction potential vs. temperature relationship was characteristic of acclimation temperature. In heterologous acclimation, the shape of this plot was related to the temperature experienced by the leg and not by the CNS. Thus acclimation was principally dependent on local tissue temperature and was relatively independent of CNS or hormonal influences.