Although the portal of entry of Cryptococcus neoformans is believed to be the lungs, viable airborne particles of C. neoformans small enough to reach the alveoli have not been observed previously in nature. Airborne particles from pigeon excreta were sampled with an Andersen sampler and a venturi scrubber. When sampled in a 6.2-liter laboratory air chamber and in a church belfry, approximately 0.01%0.33% of viable, airborne C. neoformans existed in particles with diameters between 1 μ and 5.5 μ. The demonstration of particles compatible with alveolar deposition supports the hypothesis that cryptococcosis may originate as a pulmonary infection.