Polymorphonuclear leucocyte (PMNL) migration and oedema induced by carrageenan in the pleural cavity and paw, respectively, of rats made hyper- or hypothermic by physical and chemical means have been investigated. In rats placed in a warm environment to produce a rise in body temperature, carrageenan caused a moderate but significant increase in PMNL migration compared with the control animals. Opposite effects were obtained with hypothermic animals kept in a cold environment. While hyperthermia produced by amphetamine did not alter the PMNL migration, chlorpromazine-induced hypothermia caused a fall in the number of these cells present in the pleural cavity following carrageenan. Both hyper- and hypothermias, whether induced by physical or chemical means, inhibited the carrageenan paw oedema. The observed changes in the PMNL numbers in the pleural cavity did not reflect their numbers in the peripheral circulation. Results indicate that while a rise or a fall in body temperature may have opposite effects on PMNL migration, in carrageenan inflammation both conditions inhibit oedema formation.