The present study was conducted to assess hypnotic action, effects on recta
l temperature and dose dependency by daytime administration of exogenous me
latonin (MLT) at 1 mg, 3 mg or 6 mg to subjects consisting of seven healthy
juvenile adults. As a result, exogenous MLT significantly increased total
sleep time and sleep efficiency, and MLT 6mg was observed to demonstrate hy
pnotic effects that were nearly equal to those of triazolam at 0.125 mg. Re
ctal temperature was significantly decreased at MLT 1mg and 3 mg. there wer
e no significant differences observed in the hypothermic effects at MLT 6mg
. These results indicate that exogenous MLT had dose-dependent hypnotic act
ion on daytime sleep, and it is possible to consider that this hypnotic act
ion was based on a direct-acting mechanism.