An outbreak of E. coli O157:H7 infections occurred in Sakai City, Osaka Prefecture, Japan, in July, 1996. Most of the ill were children who had attended the elementary schools in the city (total illness associated with the schools was 8355). The illnesses were associated with specific school lunches served at the schools. The epidemiologic investigation revealed that fresh white, radish sprouts, which were popularly eaten in Japan, was the food most likely associated with illness. The white radish sprouts originated from a single farm. Concurrently at least two additional outbreaks of E. coli O157:H7 occurred in neighboring areas among persons who ate the same sprouts (in a workplace with 47 ill, and retirement facility with 98 ill). The E. coli O157:H7 strains identified during these outbreaks were genetically identical. Samples of radish seeds and cultivation water were tested, but showed no trace of E. coli O157:H7. The disinfecting treatment of the seeds obviously failed to eliminate contamination.