A new Tc-99m labeled carbon particle aerosol ("Technegas") has been developed for lung ventilation scanning. This is the first reported clinical study of this agent in the United States. A total of 23 subjects were studied. Thirteen had comparative Xe-133 studies, and in seven patients pulmonary angiograms were available. The Technegas study agreed closely with the Xe-133 results in 10 out of 13 patients, while the pulmonary angiogram confirmed the Technegas and perfusion scan findings in seven out of seven cases. The Technegas scan was easily performed and well tolerated by all patients. If further clinical trials confirm these preliminary findings, Technegas may become the preferred agent for lung ventilation scanning.