SUMMARY. The pressure pain threshold (PPT), i.e. the least stimulus intensity at which a subject perceives pain, was studied in 30 patients with chronic unilateral pain in the shoulder and arm region.Fourteen trigger points were investigated on both sides of the body using pressure algometry. Eight paravertebral points and six points in the shoulder and arm region were evaluated. Each location was examined twice. The patients were tested by one examiner.The intraobserver reliability of PPT measurements was considered to be good. The Intraclass Correlation Coefficients of reliability (ICC), based on two repeated PPT measurements varied between 0.64 and 0.96. The painful side of the body was found to be more sensitive than the non-painful side, although there was not always a significant difference at the 0.05 level. The PPT was found to be higher in males than in females (P < 0.05). Females demonstrated lower PPTs than males at each trigger point. It was established that pressure tenderness varies over individual trigger points. Significant regional differences in PPT values were observed (P < 0.05). PPT values decreased in a cranial direction in the spine and in a caudal direction in the upper limb.Although the authors expected to find segmentally reduced PPT values on the painful side of the body, a generalized reduction of PPT values was present at all peripheral and spinal segmental sites. Some correlations between segmentally related trigger points were found by factor analysis. Copyright 1996 Harcourt Publishers Ltd.