The increasing reporting of Streptococcus pneumoniae resistance to penicillin has lead to the recommendation of third generation cephalospirins for the treatment of serious pneumococcal infections. As a consequence, clinicians usually do not prescribe first line antibiotics despiste the availability of susceptibility studies. Whit the aim to evaluate the impact of the infectious diseases specialist evaluation in the apropriate use oh the susceptibility studies, two series were compared: a historic control one (1998-2002, n = 50) and a prospectuve group that had the advisement of one infectious diseases specialist (2003-2006, n = 60). In both series, pneumonia stood out as the source of the bacteremia, and -alcoholism/hepatic insufficiency as associated factor. In the first series, 48 isolates resulted susceptible to penicillin by agar diffusion, and 1 out of 36 patients with pneumonia had a change in the antibiotic therapy to penicillin. In the prospective series, we found 56 susceptible isolates, and the remaining four were classified as intermediate susceptibility according to the MIC value. Antibiotics were changed in 36 out of 50 patients with bacteremic pneumococcal pneumonia (p < 0.05). The infectious diseases specialist evaluation had a positive impact on the use of the microbiological information for therapeutics purposes.