We evaluated the nucleated red blood cell (NRBC) counts in all infants with very low birth weight admitted to our neonatal intensive care unit from 1983 to 1986. There were 374 infants with birth weights of 500 g to 1500 g admitted in the first 24 hours after birth, but 31 died before studies were obtained. Of the remainder, 282 were appropriate for gestational age (AGA) and 61 were small for gestational age (SGA). Over 80% of both AGA and SGA infants were inborn and were evaluated within three hours of delivery. Nucleated red blood cell counts were significantly increased in SGA infants compared with AGA infants. The percent of infants with NRBC counts higher than 4.0 and 10.0 x 10(9)/L were 48% and 26%, respectively, in SGA infants compared with 19% and 6%, respectively, in AGA infants. Similarly, the percent of SGA infants with more than 40 or 100 NRBCs per 100 white blood cells were 62% and 36%, respectively, compared with 25% and 6%, respectively, in AGA infants. Data for specific weeks of gestation are provided and the differences were present at each gestational age. Recent data in fetuses with growth retardation, when blood was obtained directly from the fetal umbilical vein, showed an association between elevated NRBC counts and chronic hypoxemia. When increased NRBC counts are seen soon after birth, the possibility of a chronic intrauterine insult should be considered.