Electric field stimulation (EFS) causes a non-adrenergic relaxation of precontracted human airways. Only 10–20% of this response can be blocked with the nervous conductance blocker tetrodotoxin (TTX). Therefore, 80–90% of the non-adrenergic relaxation is not neurally mediated. The mechanism of this non-neural component is unclear. We examined whether EFS induces the generation of muscle relaxing substances in oxygenated Krebs-Henseleit buffer. Strips of central airways of 6 patients were precontracted with methacholine (10^–5 M) and exposed to Krebs buffer that had previously been stimulated with EFS (50 V, 0.3 ms, 30 s, 1–50 Hz). Results were compared to those obtained with unstimulated buffer. The contractile state of the airways did not change significantly with either EFS-stimulated or unstimulated buffer. We conclude that in oxygenated Krebs buffer EFS does not cause generation of substances that change the contractile state of prestimulated human airways.