<p><b>OBJECTIVE</b>To study changes in T lymphocyte subsets in preterm infants with intrauterine growth retardation (IUGR).</p><p><b>METHODS</b>The study enrolled 29 IUGR preterm infants, 38 preterm infants born appropriate for gestational age (AGA), and 20 healthy full-term infants. Peripheral blood was sampled during the first 24 hours of life, and again at a corrected age of 38 weeks of the preterm infants. T lymphocyte subsets were analyzed by flow cytometry, and absolute counts of leukocytes, total lymphocytes, and T lymphocytes were determined with an automated hematology analyzer.</p><p><b>RESULTS</b>Within the first 24 hours of life, percentages of CD3(+) and CD4(+) were lower in IUGR preterm infants than in AGA preterm infants and full-term infants (P<0.05), percentages of CD8(+) and CD4(+)/CD8(+) ratio were lower in IUGR preterm infants than in full-term infants (P<0.05), and percentages of CD3(+), CD4(+) and CD4(+)/CD8(+) ratio were lower in AGA preterm infants than in full-term infants (P<0.05). Moreover, the absolute counts of total lymphocytes were lower in IUGR preterm infants than in full-term infants (P<0.05); the absolute counts of T lymphocytes were lower in preterm infants, regardless of IUGR, than in full-term infants (P<0.05), and lower in IUGR infants than in AGA infants (P<0.05). At the corrected age of 38 weeks, percentages of CD3(+), CD4(+) and CD4(+)/CD8(+) ratio were increased in both IUGR and AGA infants as compared to the measurements within the first 24 hours of life (P<0.05), and percentages of CD3(+), CD4(+), CD8(+) and CD4(+)/CD8(+) ratio were lower in IUGR infants than in AGA infants (P<0.05), whereas there were no significant differences in counts of leukocytes, total lymphocytes and T lymphocytes between IUGR and AGA infants (P>0.05).</p><p><b>CONCLUSIONS</b>There may be a certain degree of compromise in cell-mediated immunity in preterm infants with IUGR and this compromise may last to 38 weeks after birth.</p>