Over a 4-year-period, 104 isolates belonging to the viridans streptococci were recovered from the blood and identified to the species according to Beighton and co-workers. Streptococcus oralis was the species most frequently recovered from patients in the hematology unit [29 of 39 (74%)]. Streptococcus mitis ranked second [seven of 39 (18%)]. Both species were associated with oromucositis. Isolates presently identified as S. oralis are mainly those previously identified as S. mitis or Streptococcus sanguis II. Streptococcus milleri was most frequently isolated in the patients from the general hospital population [28 of 65 (43%) isolates]: Streptococcus anginosus (n = 20), Streptococcus constellatus (n = 4), and Streptococcus intermedius (n = 4). In 14 episodes from the general hospital population, clinical significance was judged questionable. From this part of the laboratory, clinical significance could not be predicted from the number of blood cultures grown, nor from the delay of growth detection. The Rapid ID 32 Strep system agreed well with the identifications according to the scheme of Beighton et al., whereas the API 20 Strep system did not.