A method was described for detecting and counting ectopic beats using a small computer. The occurrence of an ectopic beat was identified by the relative duration of adjacent pulse intervals as demonstrated by simple arithmetical procedures. The method was validated by manual counting of records from 18 patients. Of 1474 ectopics, 89% were correctly identified. There were few false positive identifications (42). Although the method is unsuitable for the diagnosis of arrhythmias, it is likely to be of value in epidemiological studies of such disturbances.