The effect of NaHCO3 on the growth of Neisseria gonorrhoeae cultures was studied in a liquid and a semisolid growth medium. With a broth culture, NaHCO3 (0.009 M) greatly reduced the lag phase and also increased the total growth. The same concentration of bicarbonate supported rapid growth when added to the semisolid medium if the plates were individually incubated in sealed plastic bags. In a container with a large air space, a higher concentration of NaHCO3 was necessary to support growth. The assimilation of 14C-labeled NaHo3 by growing cultures was also investigated.