Serum beta-endorphin in primary fibromyalgia syndrome: a controlled study.

Serum beta-endorphin was assayed without knowledge of study subject category in 44 consecutive patients with primary fibromyalgia syndrome, 3 patients with rheumatoid arthritis (RA), and 30 normal controls, all females. Mean serum beta-endorphin levels were 81 +/- 28 pg/ml in patients with fibromyalgia, whereas those in normal controls and patients with RA were 73 +/- 17 pg/mg and 73 +/- 18 pg/ml, respectively. These differences were not statistically significant. Serum beta-endorphin levels did not correlate with relevant clinical variables in either fibromyalgia or RA groups.