Enviroxime inhibits the replication of all rhinoviruses tested in vitro at very low concentrations (10-100 ng/ml), but evaluations in humans have not consistently shown efficacy. Lack of an appropriate method for administering this water-insoluble drug may have contributed to the latter result. The present report describes the characteristics and utilization of small particle aerosols to continuously deliver enviroxime-containing liposomes (LE) throughout the respiratory tract. The enviroxime content of liposomes and biological fluids of exposed individuals was quantified by high performance liquid chromatography using C18 resin, a mobile phase of 60:40 acetonitrile:water, and monitoring at 215 nm. Small particle aerosols of LE generated by Puritan-Bennett nebulizers had mass median diameters ranging from 2.4 to 3.1 microns. The concentration of enviroxime in aerosol particles was proportional to the reservoir concentration; during the first hour of operation, the mean concentration was 20 micrograms of enviroxime/l of aerosol. Liposome particles in the reservoir, although initially heterogeneous in size (less than 0.1 to greater than 1 micron), were processed by passage through the nebulizer to smaller, more homogeneous particles; the majority were less than 0.2 micron. In a preliminary study to evaluate short term tolerance and toxicity, five volunteers were exposed to small particle aerosol of LE for 1 h. At 1 h post-treatment, large amounts of enviroxime were still present in the nasal wash as determined both by HPLC and biological assay. Enviroxime was not detected in any urine sample and was detected in only 1 of 5 serum samples. No side effects were noted. This data suggest that liposome aerosols offer a method for the delivery of hydrophobic compounds for the treatment of respiratory diseases.