Bacillus brevis strain Nagano and its gramicidin S-negative mutant, BI-7, were compared in separate as well as in mixed cultures with respect to germination of their spores in several media. Mixed-culture experiments were facilitated by the observation that colonies of wild and mutant cultures are distinctly different in appearance on nutrient agar. We found that there was complete coexistence in both strains throughout the outgrowth phase of germination, during which gramicidin S-induced suicide normally occurs in the wild-type prior to vegetative growth. Coexistence was also observed in media supporting germination but not growth, i.e., alanine-salts and alanine-water. The same was found when spores of the two strains were incubated in a soil suspension. We found that both strains become sensitive to starvation in a salts mixture only after development into vegetative cells, the mutant strain being more sensitive than the parent in this regard, but again coexistence was observed in mixed culture.