The presence of polyglucosan bodies was studied in intramuscular motor nerves of 292 muscle biopsies. These biopsies were classified into five diagnostic categories and investigated for the presence of polyglucosan bodies in relation to age and sex. Their presence was nonspecific in patients over 20 years, the only correlation being with ageing. Under 20 years, their presence pointed to the diagnosis of Lafora's disease. In cases in which both a muscle biopsy and a sural nerve biopsy were performed, the former appeared to contain these polyglucosans more frequently.