This study was designed to determine the contribution of reticular neurones in the pontomedullary reticular formation (PMRF) to the postural responses produced to compensate for an unexpected perturbation. We recorded the activity of 48 neurones in the PMRF, including 41 reticulospinal neurones, to removal of the support surface under each of the 4 limbs in 4 cats. The perturbations produced robust postural responses that were divided into 3 periods: an initial postural response (P1) that displaced the centre of vertical pressure over the 2 diagonal supporting limbs; a secondary response (P2) during which the cat restored a tripedal support pattern, and a prolonged tertiary response (P3) that maintained a stable posture over all 3 supporting limbs. Most (44/48) reticular neurones showed modified activity to perturbation of at least one limb and a majority (39/48) showed changes in activity to perturbations of more than one limb. A few (7/48) discharged to perturbations of all 4 limbs. Discharge frequency in neurones showing increased activity during P1 was relatively high (> 100Hz in 57% of the neurones responding to perturbations of either the left or right forelimbs lFl and rFL) and of short latency (17 ms for the lFL and 14 ms for the rFL). Discharge activity in most neurones was sustained throughout P2 and P3 but at a reduced level. These data show that neurones in the PMRF discharge strongly in response to unexpected perturbations and in a manner consistent with a contribution to the compensatory responses that restore equilibrium.