1. The effect of a brief train of electric stimuli in the dorsolateral funiculus on the intrinsic response properties of turtle motoneurones was investigated in transverse sections of the spinal cord in vitro. 2. Even when glutamatergic, GABAergic and glycinergic ionotropic synaptic transmission was blocked by antagonists of AMPA, NMDA, glycine and GABA receptors, dorsolateral funiculus (DLF) stimulation induced a facilitation of plateau potentials during current clamp and the underlying inward current in voltage clamp. This facilitation lasted more than 10 s. 3. The plateau potential and the facilitation by DLF stimulation was absent in the presence of 10 microM nifedipine. The DLF-induced facilitation was reduced by antagonists of 5-HT1A, group 1 metabotropic glutamate receptors and muscarine receptors. 4. These findings suggest that the intrinsic properties of spinal motoneurones are dynamically regulated by afferent synaptic activity. These afferents can be of spinal and extraspinal origin. Continuous regulation of intrinsic response properties could be a mechanism for motor flexibility.