Twenty-eight patients affected by lung cancer were studied with neurophysiological and clinical examinations to show the prevalence of alteration of neuromuscular transmission. During repetitive stimulation at 20 Hz we found in 6 cases (22%) an increment (> 20%) and in 4 cases a decrement ( > 10%) of the size of muscle action potentials. In 15 patients (57%) we found low sensory action potential amplitude (< 11 uv). In 3 (11%) of the 6 cases with incremental response the overall examination suggested a disorder of neuromuscular junction such as Eaton-Lambert syndrome. Our results suggest that the peripheral nervous system involvement in patients affected by lung cancer is higher than usually estimated.