Tissue penetration may be an important pharmacokinetic determinant to achieve the chemotherapeutic efficacy of antimicrobial agents. We describe a mouse model for the simultaneous study of antibiotic kinetics and efficacy at the site of infection. With the doses tested there was no difference in drug penetration into healthy tissue and tissue at the site of acute bacterial infection. Ampicillin and netilmicin levels over the minimal inhibitory concentration (MIC) were needed to produce significant bacterial killing. During the 6 h observation period susceptible Gram-positive bacteria were eradicated whereas Gram-negative bacteria were reduced in number but not eradicated, even though the antibiotic concentrations exceeded minimal bactericidal concentration (MBC) three times.