Bacillus larvaediffers from most nitrate-reducing species in its ability to accumulate nitrite in nutrient solutions containing but small amounts of nitrate (0.001%). Most nitrate-reducing organisms show no accumulation of nitrite at this concentration owing to assimilation of nitrate or disappearance of nitrite through reduction or assimilation. With many nitrate-reducing bacteria disappearance of nitrite keeps pace with nitrite formation only up to a certain concentration, varying with the organism, above which nitrite may accumulate.The ability ofB.larvaeto accumulate nitrite in semi-solid carrot or turnip extract media with no added nitrate is of considerable aid in the cultural test for this organism. Of five other organisms concerned with brood disease or occurring as contaminants in comb, which were grown in association withB.larvae, none showed interference with accumulation of nitrite by the latter exceptB.orpheus. With this species a positive nitrite test was dependent on the relative development of the organisms,B.larvaeexerting a certain antagonistic action. None of the eight species of bacteria tested prevented recognition of growth ofB.larvaein the semi-solid medium.