A semi-automatic apparatus for collecting microorganisms, pollen, and dust from the upper air during airplane flights is described. Findings from 45 flights near Boston are reported; 201 collections at various levels in the upper air, up to 20,600 ft. were made. Bacteria and molds were found above 19,600 ft., yeasts and pollens above 16,000 ft. Spore-forming bacteria were the predominant micro-organisms (29 spp. of bacteria were identified). Aspergilli and Penicillia were the predominating molds found. Dust counts decreased somewhat at the higher levels.