A release of endogenous glutamate (Glu), aspartate (Asp) and gamma-aminobutyric acid (GABA) from rat dorsal spinal cord slices was evoked by a 60 mM K(+)-depolarization (calcium dependent) and by 50 microM veratridine (tetrodotoxin sensitive) indicating a neuronal exocytosis mechanism. No release of the 3 amino acids investigated was obtained with the selective C-fiber excitant capsaicin (1 microM) and after impairment of afferent C-fibers the amount of amino acids released by K(+)-depolarization or veratridine was not reduced. These results suggest that amino acids may be exclusively transmitters of capsaicin-insensitive nerve structures in the rat dorsal spinal cord.