An outbreak of gastrointestinal illness occurred among attendees of a conference of cake decorators held in Michigan. Ill persons were almost five times more likely to have consumed minestrone soup than were those who were not ill. Clostridium perfringens was found in the soup and in eleven stool specimens. The soup was cooked two days prior to serving and had been improperly cooled before refrigeration; it was briefly reheated on the day it was served. This investigation demonstrated that nonanimal protein sources, such as legumes, can support substantial C. perfringens growth and should be regarded as potential vehicles in C. perfringens outbreaks.