Kaufman, J., Linington, M., Osborne, V. R., Wagner-Riddle, C. and Wright, T. C. 2015. Short Communication: Field study of air ammonia concentrations in Ontario dairy calf housing microenvironments. Can. J. Anim. Sci. 95: 539-542. The objective of this study was to measure the ammonia concentrations in the microenvironment of the calf housing area on a sample of commercial dairies in Ontario under typical management conditions. Two approaches were used to measure ammonia concentrations: (1) weekly on four farms for a period of 8 wk and (2) one-time samples were taken from the calf areas on 15 other farms. The results indicated that ammonia levels are managed below the existing maximum threshold provided in the national dairy code of practice.