The aim of this study was to determine whether procaine penicillin could be used in the treatment of suspected pneumococcal pneumonia of mild to moderate severity in an area with a high prevalence of penicillin resistance. Forty-nine patients were treated with 1.2·106 U of i.m. procaine penicillin every 12 h. By intent-to-treat analysis, 40 of 49 patients were cured and no patient died. Streptococcus pneumoniae could be demonstrated in 17 patients; 5 of 17 isolates were resistant to penicillin (MICs 0.25-4 μg/ml). Fifteen of 17 patients were cured with procaine penicillin, one presented allergy, and one was a therapeutic failure. Mean penicillin serum levels were 2.39±1.16 μg/ml (peak) and 0.61±0.38 μg/ml (trough). The results suggest that procaine penicillin may still be useful in the empirical therapy of suspected pneumococcal pneumonia.