Consumption of a specific brand of pasteurized, whole or 2 per cent, milk was epidemiologically linked to an outbreak of Listeria monocytogenes infections in Massachusetts. The risk of illness increased with the amount of milk that had been consumed. The milk used by the dairy plant originated from farms in which dairy cows were known to have been infected with listeria. In addition, listeria was isolated from raw milk samples from these farms. Inspections of the milk plant revealed no evidence of improper pasteurization technique.