Background: The rising antimicrobial resistance of streptococcus pneumoniæ, requires permanent surveillance. Antimicrobial treatments of invasive infections must be modified accordingly. Aim: To assess the in vitro antimicrobial susceptibility of streptococcus pneumoniæ strains isolated from lower respiratory infections. Material and methods: Seventy five strains isolated during three periods in consecutive years were studied. In vitro susceptibility towards penicillin, erythromycin and ceftriaxone was studied using E-test technique minimal inhibitory concentrations. Results: Five percent of strains were penicillin resistant and 11% had an intermediate sensitivity. Erythromycin resistance was observed in 1.3% of strains. Eight percent of strains had an intermediate sensitivity towards ceftriaxone and no resistance was observed. Comparing susceptibility in the three studied periods, it remained low and stable. Conclusions: High and intermediate resistance of Strepfococcus pneumoniæ towards penicillin is less prevalent than in other countries. A close surveillance must be maintained (Rev Méd Chile 2002; 130: 304-8)