The numbers of bacteria and fungi in arctic air were determined by daily sampling at Churchill, Man., during July and August 1950, and in three flights, one to Baker Lake, N.W.T., and the remainder to Resolute Bay, N.W.T. Of the three samplers which were used simultaneously the G.E. Bacterial Air Sampler gave slightly higher readings than the Bourdillon Slit Sampler, while the filter gave low readings throughout.Daily averages of bacteria at ground level ranged from 0.9 to 30.1 per cu. ft., and in the flight to Resolute Bay from 0.3 to 0.9 per cu. ft. while the comparable readings of the fungi were 0.5 to 4.4 and 0.01 to 0.7 per cu. ft. with the slit sampler. Considerable variation occurred in ground level samples, not only from day to day but throughout the day. Silicone slide studies revealed high numbers, up to 115 per cu. ft., which includes a high proportion of nonviable fungus spores. Most of the organisms are soil inhabiting forms but some fungus parasites were present, chiefly as smut (Ustilago) spores. Evidence indicates that winds originating in the south carry large numbers of organisms northward, many of which are nonviable when they reach the arctic, while north winds of polar origin contain very low numbers even in the summer.