Two groups of young, healthy, nonathletic volunteers were subjected to selective sleep stage deprivation. Six subjects were deprived of stage 4 sleep and seven subjects of REM sleep. The stage 4 deprived group reported more musculoskeletal symptoms during the deprivation condition than did the REM deprived group. The stage 4 deprived group also showed a significant increase in muscle tenderness between the baseline and deprivation conditions and an altered pattern of overnight change in muscle tenderness in response to deprivation. The REM deprived group did not show either of these changes. These results are discussed in the light of the previously postulated relationship between NREM sleep disturbance and muscoloskeletal pain in patients with so-called "Fibrositis syndrome."