Plasma immunoreactive glucagon levels (IRG), plasma glucose levels and brain and liver glycogen concentrations were analyzed in carp (adapted to 15 degrees C) subjected to short-term temperature changes (1.6 or 11 h, at 5 degrees C or 28 degrees C, respectively) and to long-term temperature changes (21 months at 28 degrees C). The high temperature (28 degrees C) produced significant increases in IRG in both short and long-term experiments. Brain glycogen also decreased in both experiments whereas liver glycogen only changed in the long-term experiment. Low temperatures did not provoke any changes either in IRG or in liver glycogen, whereas brain glycogen decreased in the 1 h exposure. In short, under these conditions in carp, IRG did not respond to low temperature but could play an important role in high temperature acclimation.