The sensitivity of the P and NP rats to ethanol was determined by the jumping test [23]. Proper interpretation of this test requires knowledge of the regional differences in the distribution of ethanol as a function of time after ethanol injection. Ethanol concentration in brain was higher than those in tail blood and skeletal muscle within the initial 30 min following the intraperitoneal injection of ethanol and was also higher than that in cerebral blood in the first 15 min. However, after 60 min, ethanol concentrations in brain and tail blood were identical. After ethanol injection (2 g/kg), the P rats jumped 88, 78, 85, 54 and 19% higher than the NP rats at 30, 60, 120, 180 and 240 min, respectively. The tail blood ethanol concentrations did not differ between the P and NP rats after 60 min. The P rats also jumped higher than the NP rats after injection of 1.5 and 2.5 g/kg ethanol. These results indicate that the P rats are innately less sensitive to the effects of ethanol than the NP rats.