Nine hundred eighty-one requests for sedimentation rates in a clinical laboratory were received and the zeta sedimentation ratio (ZSR) test was performed. The results were correlated with the patients' diagnoses and disease activity. This test was found to be a useful monitor of disease activity in a clinical setting. Substitution of the ZSR for the standard erythrocyte sedimentation rates (ESR) appears to be acceptable. The test is simple, rapidly performed, and reproducible.