Brain tryptophan is low in fibromyalgia. Intake of protein rich in large neutral amino acids is reported to lower brain tryptophan. This study was undertaken to assess whether any reduction of such proteins by exclusion of animal protein from the diet reduced pain and morbidity in fibromyalgia patients. It was an open, randomized controlled trial. 37 subjects with fibromyalgia were enrolled in the vegetarian diet and 41 in the amitriptyline groups. The outcome was assessed with the help of frequencies of fatigue, insomnia & non-restorative sleep, pain score on a 10-point VAS and tender point count. Fatigue, insomnia and non-restorative sleep were present in 41, 26 and 32 subjects before and in 3, 0 and 0 subjects respectively at six weeks of treatment in the amitriptyline group. The pain score and tender point count were 6.2 +/- 1.9 & 16.1 +/- 2.3 before and 2.3 +/- 1.3 & 6.4 +/- 3.0 after treatment. All these differences were significant (P < 0.001). In the vegetarian diet group, fatigue, insomnia and non-restorative sleep were present in 36, 24 and 27 subjects before and in 34, 29 and 29 subjects at six weeks of treatment. The pain score and tender point count were 5.7 +/- 1.8 and 15.7 +/- 2.4 before and 5.0 +/- 1.8 & 14.7 +/- 3.6 after treatment. All these differences were insignificant except that in the pain score. The decrease in the pain score, though significant, was much smaller than that in the amitriptyline group. So, it may be concluded that vegetarian diet is a poor option in the treatment of fibromyalgia.