The objective of this project was to design and build a simple, low-cost human-powered nebulizer (HPN) using locally available parts purchased in Honduras, and evaluate its clinical performance. The work was performed by students in an international engineering service-learning program at The Ohio State University. Nebulizers are used to treat people with respiratory diseases, e.g. asthma, which have a high prevalence in Honduras. Our design consists of a bicycle pump, two pump needles, plastic medical tubing, a soccer ball, air filter and a nebulizer/mask, all connected in series. A common motorcycle fuel filter serves as the air filter in the system. Pumping the foot-operated bicycle pump generates air pressure/flow in the system. The soccer ball acts as a low-pass mechanical compliance filter to smooth the time-varying pressure/flow pattern. We established a pumping frequency - 40 strokes/minute - that produced a pressure and volumetric flow rate consistent with a commercial electrically-powered medical nebulizer compressor. In a pilot study in Honduras, we compared our HPN - costing USD17 to construct from locally available parts - to a commercial nebulizer - costing several hundred dollars to purchase - as to how each improved the patients' breathing performance. We measured breathing performance before and after treatment with a standard peak-flow spirometer. Each machine improved the patients' breathing performance (p≤0.001); we found no difference in breathing improvement between the two machines (p=0.288) in this small study. Qualitatively, patients in both groups reported improved breathing performance following treatment. Our HPN is currently being used in clinics in the Choluteca region of Honduras where commercial nebulizers and the electricity needed to power them are scarce or unavailable.