This prospective, longitudinal study compared the frequency and pattern of mood changes between outpatients receiving usual care for bipolar disorder who were either taking or not taking antidepressants. One hundred and eighty-two patients with bipolar disorder self-reported mood and psychiatric medications for 4 months using a computerized system (ChronoRecord) and returned 22,626 days of data. One hundred and four patients took antidepressants, 78 did not. Of the antidepressants taken, 95% were selective serotonin or norepinephrine reuptake inhibitors, or second-generation antidepressants. Of the patients taking an antidepressant, 91.3% were concurrently taking a mood stabilizer. The use of antidepressants did not influence the daily rate of switching from depression to mania or the rate of rapid cycling, independent of diagnosis of bipolar I or II. The primary difference in mood pattern was the time spent normal or depressed. Patients taking antidepressants frequently remained in a subsyndromal depression. In this naturalistic study using self-reported data, patients with bipolar disorder who were taking antidepressants--overwhelmingly not tricyclics and with a concurrent mood stabilizer--did not experience an increase in the rate of switches to mania or rapid cycling compared to those not taking antidepressants. Antidepressants had little impact on the mood patterns of bipolar patients taking mood stabilizers.