SummaryThe respiratory activity in newborn preterm (29 days gestation) rabbits was studied after administration of thyrotropic releasing hormone. Intraperitoneal injection induced an increase in respiratory frequency (f) and a decrease in tidal volume (VT) resulting in a slight increase in pulmonary ventilation (&OV0312;E). These effects were seen in parallel to a decrease in expiratory time (TE) and respiratory time (TTOT). An increase in the TI/TTOTratio but (unaffected) VT/TIratio indicates that thyrotropic releasing hormone affects “respiratory timing” mechanisms rather than “inspiratory drive.” The changes in respiratory parameters are most probably due to an effect on the central respiratory controlling centers in the brain stem.SpeculationThe increased respiratory activity seen after administration of thyrotropic releasing hormone indicates that this tripeptide may have favourable effects in conditions accompanied by irregular or apnoic breathing during the perinatal period.