Penicillin is the drug of choice for treatment of community-acquired pneumonia (CAP) in Denmark. The primary determinant for therapeutic activity of penicillin is ''penicillin time'' (T>MIC), i.e. time with penicillin concentration above minimum inhibitory concentration. Eradication of S. pneumoniae requires T>MIC above 40-50%. The second determinant for therapeutic activity is the ratio between maximum penicillin concentration in serum and MIC (Cmax/MIC). Considering penicillin pharmacokinetics, intravenous penicillin 2 million units four times a day is recommended as empirical treatment of CAP.