A northern California sprout grower was implicated in a prolonged outbreak involving its alfalfa-clover mixed sprouts. The outbreak began with identification of a cluster of Salmonella Senftenberg cases. A case control study showed that consumption of mixed alfalfa-clover sprouts was associated with risk of illness. During the initial investigation, no Salmonella was isolated from the sprouts or the seeds. The sprout grower disinfected seeds irregularly. The sprouter was advised to stop using the seeds. However, the sprouter did not heed that advice. Between January and May, 1998, one to three additional Salmonella Seftenberg cases were identified. In June and July, 1998, twenty more cases were reported prompting additional investigation. In addition, eight cases of E. coli O157:NM were epidemiologically linked to eating the same sprouts. This time the outbreak strain of Salmonella Seftenberg was isolated from alfalfa-clover sprouts, however no E. coli O157:NM was ever isolated from the sprouts. Several related lots of clover seed but no specific lot (or related lots) of alfalfa seed could explain this outbreak. The source of the clover seeds was a distributor who obtained seeds from farms in Oregon. Ultimately 60 Salmonella Senftenberg cases and eight E. coli O157:NM were identified.