A technique for preparing casts of the macroscopic airways of mammalian lungs, which is both simplified and inexpensive in comparison with previous techniques, is described. The models are accurate, durable and flexible, and clearly demonstrate the orientation and branching pattern of the bronchial tree. The nature of the procedure also extends the availability of casts to laboratories or individuals with limited instrumentation and/or funding. Preliminary results using this technique to inject the lungs and certain air sacs of birds are also discussed.