The effect of total sleep deprivation for one night on the depressive state (measured using the depression rating scale of Bojanovsky and Chloupkova) and the patients' actual state of well being (measured using the self-rating scale of von Zerssen) is investigated in a group of 40 randomly selected inpatient depressives (29 endogenous depressives, 11 neurotic depressives) over a period of 36 h. The endogenous depressives exhibited a statistically significant change. The total index of the depression scale improved by 22.6%, recorded as a 'daily mean difference'. The individual symptoms of depressive mood, lack of interest, inhibition and inappetence were significantly improved. The feature of vital disorders and its common appearance with diurnal variations correlates positively with the degree of sleep deprivation effect. The symptomatology of the neurotic depressive patients also showed a significant improvement but the relatively small group of particularly severe neurotic depressives who also exhibited vital disorders is not representative. In a group of cases, sleep deprivation caused reversion in the depressive symptomatology not only during the night of deprivation but influenced the diurnal rhythm of the depressive symptomatology on the following day, in a therapeutically favourable direction. The results are compared with those of other studies. The methodological problems are discussed and methodological improvements for further investigation are proposed.