Technical Abstract: The stabilization of living microbial agents for use as biological control agents is often accomplished through desiccation. The drying process must be conducive to the survival of the living microbial agent during desiccation and storage. Our air-drying studies with liquid culture-produced blastospores of the entomopathogenic fungus Paecilomyces fumosoroseus have shown that the relative humidity (RH) of the drying air significantly impacts the desiccation tolerance and storage stability of these propagules. Drying air with RH above 40 percent was shown to support high rates of initial blastospore survival (~80 percent) after drying; and drying air with RH above 55 percent, significantly improved the shelf-life of the blastospore preparations. The pH of the spent medium or the rinsing of spent media from the blastospore preparation prior to air-drying had no significant impact of blastospore desiccation tolerance. A lab-scale, air-drying chamber that delivers air flow over the sample and that can be operated at controlled-relative humidity is described.