Objective: To compare the effects of two antidepressants on exercise performance of the female patients with fibromyalgia. Methods: Fifteen patients with fibromyalgia participated in this randomized, double-blind crossover study composed of two trials separated by a 2-week washout phase. The pharmacy randomly assigned patients to two groups: (a) placebo (glucose) in the morning and 25 mg amitriptyline at bedtime or (b) 20 mg fluoxetine in the morning and placebo at bedtime. The VO2max and Wingate anaerobic test were evaluated. Within 24 h after 15-day medication, the tests were repeated. Results: Peak power and fatigue index increased, and VO2max and VT did not change with both fluoxetine and amitriptyline. Mean power significantly increased after fluoxetine but not after amitriptyline. Conclusion: Both amitriptyline administration and fluoxetine administration in patients with fibromyalgia have beneficial effects on anaerobic performance. These effects may be important in life quality of the female patients with fibromyalgia. © Clinical Rheumatology 2005.