Responses of dorsal horn neurons to bath application of substance P, somatostatin and enkephalin were studied by intracellular recording in the neonatal spinal cord slice preparation. Substance P depolarized dorsal horn neurons and increased their excitability. The depolarization was most commonly associated with an increase in neuronal input resistance. Somatostatin and enkephalin hyperpolarized dorsal horn neurons and caused reduction or abolition of spontaneous firing. While the hyperpolarization produced by enkephalin was always associated with a fall in neuronal input resistance, in the case of somatostatin the similar effect was less consistently observed.