A method for applying 99mTc-MDP for dynamic and static quantitative radioisotope scanning (QRS) of the sacroiliac joints (SI) in early progressive sacroiliitis in ankylosing spondylitis (AS) is described. In a prospective study, 2 groups of male AS patients were investigated, one with increased elevated erythrocytic sedimentation rate (ESR) (group A, n = 7) and one with normal ESR (group B, n = 8). In both groups an increased uptake of the radiotracer was found in the static part of the study versus a control group C (n = 9). An increased uptake versus group C was also found for group A in the dynamic part of the study (p = 0.01) while there was no significant difference dynamically between groups B and C. The results of the dynamic study in group A indicate ESR to be a parameter of inflammatory activity in the SI joints. The study also seems to indicate QRS to be a valuable diagnostic method in early AS without definite radiographic changes in the SI joints.