• Percentile curves were calculated for hemoglobin; hematocrit; total red and white blood cell counts; mean corpuscular volume; mean corpuscular hemoglobin; mean corpuscular hemoglobin concentration; and platelet, neutrophil, band cell, lymphocyte, monocyte, basophil, and eosinophil counts in preterm babies of 24 through 36 weeks' gestation. The curves were derived from mainly Saudi Arabian preterm babies who were born in Riyadh, which is just above sea level. Babies born to mothers with hematologic problems or babies who themselves had any evidence of hematologic disorder, blood loss, or disorders that affect hematologic values, eg, asphyxia, were excluded from the reference population. Six hundred two newborns were included in the study; however, after exclusions, the final reference population was 550. A minimum of 50 babies were studied for each gestational age except for gestations of 24 and 25 weeks. For these two gestations, 27 and 21 babies were studied, respectively. The percentile curves should be useful as a guide to the normal range of these variables in babies, particularly those of Arab origin.