To diagnose sporadic diarrhoea due to Clostridium perfringensinfection, faecal specimens from elderly patients were examined directly for C. perfringensenterotoxin using reverse passive latex agglutination assay, and then cultured for this organism. C. perfringensisolates from those samples were grouped by slide agglutination and by pulsed‐field gel electrophoresis (PFGE). Fifty of the 60 isolates agglutinated with newly raised antiserum WX2 and 38 shared the same genomic PFGE pattern. Characteristics of the epidemics and experimental data suggest that the diarrhoea was caused by a nosocomial spread of C. perfringens, and not by a food‐borne outbreak.