A red strain of B. intermedium was found to excrete a factor (factor R) which can specifically induce conjugating pairs in cells of an albino strain of this species. This factor appears to be a heat stable substance of low molecular weight. The albino strain was found to excrete the other factor (factor A) which can specifically induce conjugating pairs in cells of the red strain and probably also can promote the production of factor R in red cells. Factor A appears to be a heat unstable substance of high molecular weight.