There have been few clinical reports on pharmacokinetics-pharmacodynamics (PK-PD) theory, although many basic or fundamental researches on appropriate use for the antimicrobials based on the PK-PD theory have been performed. We evaluated the target T>MIC values on meropenem and biapenem which have been obtained by basic researches. While we investigated whether the target T>MIC values were also useful for anaerobic infections. Clinical and bacteriological efficacies of meropenem and biapenem were about 70% in T>MIC over 25% or over 80% in T>MIC over 30%. When monomicrobial infections by anaerobes were occurred as abscesses, there have been no correlation between target T>MIC values and clinical effect. When polymicrobial infections between aerobes and anaerobes were occurred, we have achieved over 90% clinical efficacy when over 20% T>MIC values. These results supported the data by Craig, W. A. and Drusano, G. L. The regimen based on PK-PD theory would be useful in clinical practice including against anaerobic infections.