Experiments were designed to assess the mechanisms of diisopropyl fluorophosphate (DFP)-induced changes in thermoregulation of the rat. In one study, male rats of the Long-Evans strain were injected with DFP (s.c.) at doses ranging from 0 to 2.0 mg/kg while maintained at an ambient temperature (Ta) of 20-24C. Body (Tb) and tail skin (Tt) temperatures were recorded for 5 h post-injection. DFP doses of > or = 1.0 mg/kg resulted in significant decreases in Tb lasting up to 5 h and increases in Tt lasting up to 1 h post-injection. In a second study, metabolic rate (MR), evaporative water loss (EWL), motor activity (MA), Tb, and Tt, were measured at 2 h post-injection of 0, 0.5, 1.0, and 1.5 mg/kg DFP (s.c.) at Ta values of 10, 20, and 30 C. DFP treatment resulted in hypothermia at all three Ta values, but the effect was attenuated at 30 C. MR was significantly reduced at a Ta of 20 C following 1.5 mg/kg, unaffected by DFP at a Ta of 30 C, and stimulated at 10 C following 0.5 mg/kg DFP. EWL was significantly elevated at 30 C following 1.5 mg/kg DFP. MA was significantly reduced following > or = 1.0 mg/kg DFP at 20 and 30 C and 1.5 mg/kg at 10 C. Tt was elevated and reduced by DFP at Ta values of 30 and 10C, respectively. In a third study, rats were injected with DFP and placed in a temperature gradient for 1 to 2 h post-injection while selected Ta and Tb were monitored. While both control and DFP-treated rats remained in the cool end of the gradient, rats administered DFP at doses of 1.0 and 1.5 mg/kg were significantly hypothermic. (Copyright (c) 1991 Elsevier Scientific Publishers Ireland Ltd.)