Objectives. To study possibilities of immunological and electrophysiological methods for the diagnosis of paraneoplastic polyneuropathy in cancer. Methods. We studied 88 cancer patients using electromyography and immunological assay (serum neuronal antibodies). Results. A symmetrical, distal, sensory-motor, axonal-demyelinating form of polyneuropathy can develop in breast cancer and small cell lung cancer. Onconeural antibodies were detected in the serum of more than half of study participants as well as in some healthy donors. Symptoms of polyneuropathy appeared earlier than the diagnosed tumor. Conclusion. The diagnostic value of the methods used for the early diagnosis of breast cancer and small cell lung cancer is emphasized.