The zeta sedimentation ratio (ZRS) was evaluated and found to have advantages over the erythrocyte sedimentation rate (ESR). The normal range for the ZSR proved to be 41 to 54%. Elevated ESR's obtained with the modified Westergren technic were also associated with an increased ZSR, except when amenia spuriously elevated the ESR. Reproducibility after storage was slightly better for the ZSR than for the ESR, But for optimal results the test should be performed within two hours of phlebotomy. Increased concentrations od EDTA anticoagulant may falsely elevate the ZSR, especially if the ZSR is initially elevated.