Recent data have suggested a correlation between the tenderness measured at tender and control sites, differing from earlier studies indicating site specific tenderness. In our study, the "constant control" model is tested against the "correlated control" model, in which control site tenderness varies with fibrositic site tenderness. Our study also addresses relevant technical issues in dolorimetry. We measured threshold of tenderness at 4 sites (2 fibrositic and 2 control) on 21 subjects, using dolorimeters with a 17 kg scale limit, and 3 different footplates, 0.7, 1.4 and 2.0 cm in diameter. To measure observer variation, we used multiple replications by multiple observers, obtaining in all 1,416 observations. There was a strong relationship between control and fibrositic site tenderness with control thresholds twice as high (half as tender). Scale length and dolorimeter footplate size each had important effects. The site specific approach is valuable diagnostically, but more broadly operative mechanisms should be the focus of research and therapy.