Twenty patients with fibromyalgia syndrome (FMS) and 20 matched healthy controls were subjected to an exercise stress test above their anaerobic threshold. Serum samples for the measurement of growth hormone (GH), insulin-like growth factor-1 (IGF-1), prolactin (PRL), adrenocorticotrophic hormone (ACTH) and cortisol were taken prior to and after the test at 30-min intervals. Compared to the controls, the patients with FMS displayed significantly lower basal GH levels and slightly, though significantly, higher prolactin levels. Following the exercise test there was a significant increase in the mean GH level in the patient group (P = 0.0474) and a significant decrease in the control group (P = 0.0286) 1 hour after the exercise. A slight decrease in ACTH levels in the control group was observed (P = 0.0002), but there was no significant change in FMS patients. Cortisol levels were significantly lower in both groups after the exercise (P = 0.0001). These results suggest the possibility of a perturbation in hormonal response to exercise in patients with FMS.