To test the hypothesis that the antidepressant effects of total sleep deprivation (TSD) are linked to the serotonergic and/or noradrenergic system the authors carried out a double-blind study (fluvoxamine versus maprotiline) in 42 inpatients with endogenous depression (ICD). Patients were randomized to a four-week treatment with either fluvoxamine (100-300 mg/day) or maprotiline (100-300 mg/day). In addition, patients underwent a TSD procedure before and after one week of antidepressant medication. There was a statistically significant reduction of depression ratings (HDRS) in both the fluvoxamine and maprotiline group. The day-1 response to TSD before antidepressive medication was not associated with a clear relationship to the outcome after four weeks of treatment with either fluvoxamine or maprotiline. On the other hand, the day-2 response to TSD was significantly correlated with a good outcome to subchronic treatment with maprotiline. Furthermore, the results of the authors' data suggest that a favorable short-term outcome of TSD may be connected to antidepressants enhancing the serotonergic neurotransmission. The global comparison between fluvoxamine and maprotiline revealed that the group of patients treated with fluvoxamine had a significantly higher efficiency index (CGI) than the maprotiline group; fluvoxamine was rated to be tolerated excellently in 70% of the patients whereas this percentage was only 43% in the maprotiline group. There was also significantly more vertigo and dry mouth in the maprotiline group whereas the fluvoxamine group was rated to have significantly more sleep disturbances during the trial.