Quantitative sacroiliac scintigraphy was performed in 33 patients with ankylosing spondylitis (AS), 34 patients with nonspecific low back pain, and 30 control subjects. Significantly increased uptakes over the sacroiliac joints (SIJ) were found in patients with AS and in patients with degenerative changes of the SIJ. No significant differences were found between patients with mechanical low back pain by lumbar strain or by degenerative changes of the lumbar spine and the control subjects. But there were 2 of 13 patients with low back pain by lumbar strain with pathologic uptakes over the ISG. Since the scintigraphic technique is not specific, it is necessary to compare the scintigraphic results with clinical and radiological findings in each patient. On this condition sacroiliac scintigraphy is useful in early diagnosis of AS.