We present a review of 229 blood cultures with viridans streptococci collected during a period of eight and a half years from 1986 to 1994 at a teaching hospital in Sweden. The clinical significance of the growth of viridans streptococci is always uncertain, since these bacteria can be contaminants from the skin flora. Growth in more than one culture bottle strengthens the clinical value of the finding. The question was whether species identification might also help in the assessment of the clinical relevance of the finding. The results show that Streptococcus mitis occurs significantly more frequently in blood cultures from the departments dealing with cancer patients. Even with polymicrobial growth in blood cultures, S. mitis should be considered a pathogen of clinical relevance, not a contaminant.