Thirty-three premature and full-term infants (PCA, 31.5 to 50 weeks) who were free from neurologic and cardiopulmonary disease at the time of testing underwent a standardized TAS test during polygraphically controlled REM sleep. The R-R interval and the TTOT were measured before and during TAS. The R-R interval and TTOT changes during TAS were compared to the preceding 60-second mean R-R interval and TTOT in each infant and expressed as a percentage of mean control values (ie, % RR and % TTOT). During TAS, there was a significant negative correlation between cardiac and respiratory responses and postconceptional age (p less than 0.001 and p less than 0.0001, respectively). Prolongation of both the R-R interval and the TTOT elicited by TAS was significantly blunted by maturation.