A comparison of the micro- and macroerythrocyte sedimentation rate methods performed in disposable polystyrene tubes using venous blood from 524 pediatric patients demonstrates an excellent correlation between the methods. The micromethod produces values higher than the macromethod at values above 10 mm/h but this difference is not of sufficient magnitude at the clinical decision level to warrant a change in the traditional reference ranges. The mean difference between the two methods in the 10-25 mm/h range is 1.4 mm/h. The high bias of the micromethod is accentuated in samples with hematocrits less than 30%. The micro- and macromethods do not maintain a constant relationship throughout the range evaluated.