Push-pull cannulae were acutely positioned through previously implanted guides in the globus pallidus of unanesthetized freely moving cats and rats. During slow-flow perfusions, enkephalin release was detected in resting conditions and increased more than 3-fold when both 50 mM K+ and 1.8 mM Ca2+ were present in the perfusing medium. Local perfusion with veratrine also enhanced enkephalin release. Furthermore, in vivo, electrical stimulation of the rat caudo-putamen enhanced enkephalin release in the pallidum. This latter finding is consistent with a functional strio-pallidal enkephalin-containing pathway previously postulated by immunohistochemical or lesion experiments.