A procedure is described for the direct collection of bronchial or tracheal fluid samples on to paper discs. Using the procedure, the pharmacokinetics of ceftazidime in rabbit bronchial and tracheal fluids were compared with those in the respective wall tissue samples and in lung tissue. Concentrations appearing in lung tissue were approximately half those seen in bronchial or tracheal fluid or bronchial and tracheal wall tissue. Concentrations in these latter compartments were, in turn, four- to six-fold lower at all times than simultaneously-measured serum levels. The shape of the concentration/time curves were similar for all compartments sampled. The half life values were 63 to 64 min for respiratory tract concentrations and 59 min for serum levels. Percentage penetration from serum into the various compartments was 20.8% for bronchial fluid, 19.9% for tracheal fluid, 22.4% for bronchial wall, 20.0% for tracheal wall and 11.3% for lung tissue.