We have used the new Technicon H.1 Hematology Analyzer to determine the indices of erythrocytes obtained from 18 nonthalassemic (alpha alpha/alpha alpha genotype) adult patients with Hb SC disease. Controls were 14 normal black adults and 29 white adults. The data showed that SC erythrocytes are significantly smaller than normal RBC (P less than .001) with a significantly higher MCHC value (P less than .001) than controls. These features of SC RBC could not be reproduced by an Ortho ELT-8 electronic counter. Hb SC erythrocytes have unique indices which are best demonstrated either by semimanual methods or by the H.1 system.