The reference ranges for the newborn hemogram during the first 58 h of life were developed from blood counts generated from 200 healthy neonates (61 African-Americans and 139 Caucasians). The mean age was 41.9 h (range 2.0-57.9) and weight 3.4 kg (range 2.0-4.7). In the African-American neonates, the average (+/-2SD) hemoglobin (HGB) concentration was 19.4g% (14.0-23.5), mean corpuscular volume (MCV) 100.5fl (85.3-110.7), white blood cell (WBC) count 15.4 x 10(3)/mm(3) (8.9-23.3), absolute neutrophil count (ANC) 8.6 x 10(3)/mm(3) (3.2-14.9), and absolute band count (ABC) 262/mm(3) (0-1,261). The corresponding values for the Caucasians were: HGB 20.2g% (16.0-24.6), MCV 104.6 fl (95.9-112.8), WBC count 17.0 x 10(3)/mm(3) (10.4-27.1), ANC 9.2 x 10(3)/mm(3) (4.3-18.2), and ABC 365/mm(3) (0-1,677); only the differences in the HGB (p < 0.03), MCV (p < 0.001), and WBC count (p < 0.03) reached statistical significance. In addition, the African-American neonates had lower absolute eosinophil (AEoC) (p < 0.0001) and lymphocyte (ALC) (p < 0.03) counts. Gender had no significant effect on the hemogram parameters. Age (from 2 to 58h) had statistically significant effect only on the WBC count, ANC, and nucleated red blood cell (NRBC) count (p < 0.01).