Quantitative sacroiliac (SI) scintigraphy was performed 3 h after an i.v. injection of 16 mCi 99mTc-EHDP. The resulting images were recorded and processed and on an ON data system 150. Five technical approaches for objective digital assessment of abnormal uptake of the tracer at the sacroiliac joints were employed. SI indexes from the ratio of radioactivity in the SI joints and in the os sacrum, determined either by a region-of-interest technique or by a profile-scan technique measuring the maxima of the curve over a defined base line, proved to be the best parameters in discriminating normal from abnormal uptake of the radiotracer in the SI joints. The quantitative scan technique appears to be useful as an objective tool in interpreting SI scans.