Blakeslea trispora. a filamentous fungus. Was cultured with or without accompanying strains of Micrococcus luteus. Bacillus subtilis, Streptomyces fradiae. And Saccharomyces cerevisiae which were added separately to 24 h old cultures. in order to increase beta-carotene production. It was shown that by adding M. luteus. the β-carotene production in the culture medium was increased about 2.7 times -in comparison to control. B. subtilis and S. fradiae showed no considerable effect on β -carotene production while S. cerevisiae had a negative effect. M. luteus was then added to unmated plus and minus types of B. trispora leading to a little increase in beta- carotene production compared to the control. The positive effect of adding M. luteus was only due to the existence of its life cells. Since addition of autoclaved or cell-free culture supernatant of this bacterium did not increase the beta-carotene production in B. trispora cultures.