Peak-ratio interference pattern analysis (peak-ratio method) is said to have a high sensitivity and to be independent of sex and age. This study was carried out to prove or disprove these findings. The peak-ratio method and qualitative motor unit action potential (MUAP) analysis were applied to the right brachial biceps and anterior tibial muscles of 44 healthy subjects, aged 23-87 years, 25 neuropathy patients, aged 21-83 years, and 29 myopathy patients, aged 19-70 years. Peak-ratio parameters were independent of sex and age. They tended to be lower in the anterior tibial muscle than in the brachial biceps muscle. Neuropathy patients typically showed decreased peak-ratio, short time intervals and increased amplitude/turn. Myopathy patients typically showed increased peak-ratio, turns/s and short time intervals. The sensitivity of the peak-ratio method was 72% for neuropathy patients and 59% for myopathy patients. The sensitivity of the peak-ratio method was similar to that of the MUAP analysis in neuropathy patients and higher than that of the MUAP analysis in myopathy patients. The specificity of the peak-ratio method was 80%. The peak-ratio method proved to be a valuable, supplementary electromyographic tool for the detection of neuromuscular disorders.