The effects of stimulating (NaCN, ACh, eserine and haloperidol) and depressant (zero [Ca2+]o, mecamylamine and dopamine) agents of carotid body chemoreceptors were tested at different temperatures. Temperature was varied between 29 and 39 degrees C and Arrhenius plots of the sensory discharge frequency against the reciprocal of absolute temperature were constructed before and during application of the chemicals. NaCN, ACh and zero [Ca2+]o did not change the apparent activation energy (mu) whereas eserine, haloperidol and probably mecamylamine depressed mu. Dopamine probably increased mu. Thus, there were no uniform effects of temperature on the action of different chemosensory stimulants or depressants, suggesting that these agents act on different steps of a chain reaction.