Previous findings showed that, in a subgroup of patients administered heterogeneous antidepressant treatments, perceived mood levels during a major depressive episode fluctuate with day to day changes which follow cyclical patterns (termed "minicycles"). We investigated the predictability of infradian mood fluctuations during acute depressive episodes in patients standardly medicated with fluvoxamine. We applied time series analysis, by means of autocorrelation techniques, to time lagged serial recordings of perceived mood levels of 20 inpatients (13 Major Depression Recurrent, and 7 Bipolar Depressive Disorders). 5/20 patients exhibited predictable cyclical patterns in their perceived symptomathology, 8/20 exhibited an uneven, sawtooth pattern of progressive amelioration, and 7/20 showed an erratic pattern of unpredictable day-to-day variations. We confirmed the existence and the predictability of cyclical mood patterns in a subgroup of patients. The absence of a linear improvement in perceived mood did not worsen the final response to antidepressant therapy.