Measurements of concentration of bacterial aerosols using a filtration method were made in calf hutches as well as in a dairy barn, a heifer barn, and a barn housing cattle of all ages. The concentration of bacterial aerosols inside calf hutches was 59 BCFP/10l in summer and 22 BCFP/10l in winter, which was markedly lower than that in the other barns. The differences in the concentration between calf hutches and the other barns were more obvious in winter than in summer. The concentration of bacterial aerosols around and between hutches was very low and nearly equal to that of the outside environment. These results indicate that calf hutches provide a higher degree of air purity than do the other barns tested and that calves in calf hutches can be raised in nearly isolated conditions with respect to air-borne infection.