Most Bacillus species are unpigmented. Some strains of Bacillus megaterium are known to form a yellow pigment especially on casein agar.the presence of Bcilli in ileal and fecal sample prometed me to study in more details those organisms. I found that many of those organisms are pigmented with colors ranging from yellow, to pink and red, the appearance of the colors seemed to be regulated by a nutrient and/or cell density signals. this was a surprising finding since only few species of the Bacillus genus have been reported as pigmented. In addition, since Bacilli are not photosynthetic species, the presence of pigments raised questions about their functional role.Other laboratories,identified this pigment produced by several Bacilli as carotenoid. we attempt to understand their physiological role.One of the isolates, belonging to the Bacillus pumilus, was particularly interesting because the pigment was water-soluble and was produced in a temperature-regulated fashion.