The concentration-time curve of ciprofloxacin has been assessed in the blood compartment and in the lung tissue following oral administration of the drug. Immediate release and erosion-controlled dosage forms have been examined. A numerical model based on finite differences and taking into account all relevant data has been built: the kinetics of drug release in the gastrointestinal tract, drug absorption in the blood compartment and elimination, and the transient diffusion of the drug through the lung tissue. A partition coefficient for the drug at the tissue-blood interface has been considered to express the drug concentration at the tissue surface. The effect of dose frequency and erosion rate on the antibiotic versus time curves in the plasma and the lung tissue has been studied in detail.