To determine reference values of red blood cell counts in a Coulter S-Plus STKR, we studied 122 males and 147 females selected from the hospital staff (physicians, chemists, nurses) and blood donors. Their ages ranged from 17 to 45 years. Iron and total iron binding capacity in serum, and Zn-protoporphyrin and folates in erythrocytes were measured to include only normal subjects without nutritional deficiencies. Two males (1.6%) and 21 females (14.3%) were excluded due to iron deficiency, and one man (0.7%) and one woman (0.8%) to folate deficiency. All red cell parameters, except the mean cell volume, showed a gaussian distribution (Lilliefors test). Their mean +/- standard deviation were: [formula: see text].