Some problems in the use of the Coulter counter for erythrocyte total counts and volume distribution.

Normal erythrocytes were subject to swelling and some haemolysis when suspended in a NaCl-formaldehyde-Na(2)EDTA diluent of pH 4.9 for routine blood-cell counting in the Coulter counter. A phosphate-buffered saline of pH 7.4 was substituted and has proven satisfactory for total erythrocyte counts. Polyvinyltoluene latex was unsuitable for volume calibration of the counter, because of aggregation of the particles in saline. Ragweed pollen grains gave a calibration factor that agreed well with that for fresh erythrocytes. Recent batches of Dade's Erythro-Trol (a suspension of fixed erythrocytes) were satisfactory for both total counts and volume calibration.