Long sleep (LS) and short sleep (SS) lines of mice were derived from a heterogeneous stock of mice (HS) and have been selectively bred on the basis of the time the animals were devoid of the righting reflex (sleep time) following acute ethanol administration. We have tested a large group of the HS mice for sleep time response to ethanol. Animals were then selected from the extremes of the HS sleep time response and designated short sleep (HS-SS) or long sleep (HS-LS). The ED50 value for loss of righting reflex was compared between these mice (HS-SS and HS-LS) and animals that had undergone 25 generations of selection (SS and LS mice). The ED50 value was not significantly different for the HS-LS (1.9 g/kg) and LS (2.17 g/kg) mice but was markedly different between HS-SS (3.02 g/kg) and SS (4.21 g/kg) mice. The ED50 values for the eight inbred strains that constituted the HS stock ranged only from 2.33 to 2.78 g/kg. The value for LD50 one hour after ethanol administration was found to be 9.03 g/kg and for SS mice 6.94 g/kg for LS mice, in contrast to our previous findings of no difference in LD50 values between SS and LS mice when ascertained 24 hr after the ethanol dose. Since the two lines were selected only for a sleep time difference, a differential sensitivity to other consequences of acute ethanol exposure, such as the lethal dose, would not be expected unless the effects shared a common genetic mechanism of action with ethanol sleep time.(ABSTRACT TRUNCATED AT 250 WORDS)