The performance of the Technicon H*1™ was evaluated in the computerized, high-volume hematology laboratory at M. D. Anderson Hospital and Tumor Institute and compared with that of reference instrumentation used for routine patient care. The precision, linearity, and lack of carry-over of this instrument was excellent for the entire dynamic range of all nine tested parameters (white blood cells [WBCs], red blood cells [RBCs], hemoglobin [Hgb], hematocrit [Hct], mean corpuscular volume [MCV], mean corpuscular hemoglobin [MCH], mean corpuscular hemoglobin concentration [MCHC], red blood cell distribution width [RDW], and platelets [Plts]). Coefficients of correlation for all directly measured parameters were always 0.98 or greater, with the exception of the MCV and RDW parameters, for which r = 0.89 and 0.93, respectively. Special emphasis was placed on WBC and Pit counts at low ranges. When compared with reference methods the correlation for both parameters was very good, r = 0.99 for WBCs less than 4.0 × 103/μL (4.0 × 109/L) and 0.91 for Pit less than 100 × 103/μL (100 × 109/L). These excellent performance characteristics for the CBC parameters, combined with the ability of the analyzer to perform a full WBC differential (to be described in the next report), make the H*1 a superior advancement in the field of automated hematology.