There was good agreement between results obtained with Coulter VCS/Technicon H1 and manual counting with respect to neutrophils and eosinophils. Coulter VCS overestimates the lymphocyte percentage compared to manual counting and to H1. If, however, the percentage of so called "naked" cells are added to the percentage of manually counted lymphocytes, the agreement between VCS and the manual method is improved. The alarms given by the two instruments are of little value in detecting left shift or nucleated red blood cells.