The whole cell patch-clamp technique was used to investigate whether there were inwardly rectifying K⁺ (K_ir) channels in the longitudinal muscle of cat esophagus. Inward currents were observable on membrane hyperpolarization negative to the K⁺ equilibrium potential (E_k) in freshly isolated esophageal longitudinal muscle cells. The current-voltage relationship exhibited strong inward rectification with a reversal potential (E_rev) of 76.5 mV. Elevation of external K⁺ increased the inward current amplitude and positively shifted its E_rev after the E_k, suggesting that potassium ions carry this current. External Ba²⁺ and Cs⁺ inhibited this inward current, with hyperpolarization remarkably increasing the inhibition. The IC₅₀ for Ba²⁺ and Cs⁺ at 60 mV was 2.9 and 1.6 mM, respectively. Furthermore, external Ba²⁺ of 10 µM moderately depolarized the resting membrane potential of the longitudinal muscle cells by 6.3 mV while inhibiting the inward rectification. We conclude that K_ir channels are present in the longitudinal muscle of cat esophagus, where they contribute to its resting membrane potential.