Excipient-free isoniazid aerosol formation and pulmonary delivery in mice are studied. An evaporation-nucleation route is used for the generation of isoniazid aerosol. Particle diameters and number concentrations are measured with an aerosol spectrometer consisting of a diffusion battery, condensation chamber, and photoelectric counter. The pulmonary delivery of isoniazid particles is studied in both nose-only (NO) and whole-body (WB) inhalation chambers for the particle mean diameter and number concentration to be 600 nm and 6 × 10 6 cm −3 , respectively. It is found that the rate of drug systemic absorption in the WB chamber is 27% higher than that for the NO one because of an additional consumption of drug orally from the fur in the WB chamber. The particle deposition efficiency ε in the mouse respiratory tract is measured as a function of mean diameter. The quantity ε is equal to 0.7 for the particle diameter d = 10 nm and decreases to 0.2 with the diameter increasing to 300 nm, and then, at d > 300 nm the deposition efficiency increases with diameter to 0.5 at d = 2000 nm. The bioavailability of the aerosol form of isoniazid (72 ± 10%) is very close to that for the per-oral form (61 ± 10%).