Subjective sleep ratings and polygraphic sleep parameters were recorded for 76 nights in 5 young and 3 old subjects in a noisy urban apartment (46.67 dB(A)) and in a quiet rural house (27.72 dB(A)), in order to clarify the difference between the sleep of the young and that of the old. The results were as follows. Both sleep period time (SPT) and total sleep time were longer for the young than for the old in a quiet bedroom. Both REM latency and sleep latency did not differ significantly between the young and the old. Mean sleep depth was shallow for the old because of more time for wake after sleep onset and stage 1 sleep and less time for slow wave sleep. There was no significant difference of stage 2 sleep between the young and old. The percent of REM in SPT were less for the old. The old subjects reported that they had less dreams than the young. The sleep of young was a little more susceptible to road traffic noise than that of old. In the elder subjects, "Couldn't sleep well" was found to be the most valid parameter of the quality of sleep, though "Difficult to fall asleep" was the most representative in the young.
