Streptococcus milleri is unique among the viridans streptococci because it produces abscesses. Five serious S. milleri infections were seen in our hospital in 1 year. The English literature dealing with S. milleri was reviewed. An infection caused by S. milleri is often associated with a gastro-intestinal source. Thus, the speciation of viridans streptococci from pus or blood cultures is clinically relevant. The identification of S. milleri from blood cultures suggests the possibility of serious purulent infection, the source of which may lie in the gastro-intestinal tract. The resultant clinical approach to S. milleri infection is discussed.