As against the expectations, combined inoculation of both the bacteria had no significant effect on black gram growth, compared to uninoculated control. But it is evident from PCR analysis that both bacteria have colonized root tissues. The growth stage of seedlings we observed may be too early (5 days old) to visualize significant growth effect. However, the possibility for physical co-colonization without physiological effects cannot be also neglected. P. fluorescens and B. subtilis being biocontrol agents may start producing/inducing compounds inside plant tissue after establishment. Nevertheless, our observations have provided preliminary evidences for compatibility of these two bacteria in co-aggregating in culture and co-colonizing in plant roots.