Erythrocyte Sedimentation Rate (ESR) is a simple, non-specific clinical test. Most models of erythrocyte sedimentation (ES) are formulated as a sigmoid function but consider the ES process to consist of three distinct phases: single-cell fall; fall of rouleaux and aggregates; cell packing. Recently, a piecewise (three-phase) continuous model has been developed. Our study applies ES data from 29 haematologically normal subjects to this model and re-evaluates the mechanism of ES using the derived model parameters. Using the Westergren technique, ES readings were taken every 10 minutes for 300 minutes. Three subjects remained in the first phase, while 26 displayed three discrete phases. For the 26 subjects, the average rate of fall of the sedimenting particles in the first phase 87 microns/min, while that of the second phase was 176 microns/min. The ratio of these two values suggests an alternative nature of sedimenting particles in the first phase. Further, the average duration of the first phase was 62 minutes, suggesting that, in 50% of subjects, aggregate formation is incomplete when ESR is measured at 60 minutes.