Johnstone, D. B. (University of Vermont, Burlington). Growth of Azotobacter in deuterium oxide. J. Bacteriol. 83:867–870. 1962.—To the small list of bacteria that are reported to have been cultured in fully deuterated media can be added Azotobacter agilis and A. vinelandii. Moreover, these bacteria, although growing in a deuterium oxide medium with deuterated carbon sources, will fix atmospheric nitrogen. Lag periods occur prior to growth, and wide morphological variation is apparent during adaptation to a deuterated environment. A convenient method is presented for measuring, by infrared spectroscopy, the amount of water that accumulates in a D2O medium; during incubation this amounts to about 1% per day. Prevention of this accumulation of water indicates that growth, after a lag period, probably is not supported by accumulated hydrogen.