The population composition of polycultures of Pseudomonas aeruginosa dissociants (R + M and R + S + M) developing on media with various contents and ratios of nitrogen and phosphorus has been studied. Irrespective of its proportion (10 to 90%) in the inoculum, the R variant accounted for 65 to 84% of the whole population of linear-phase and stationary-phase binary cultures of R and M dissociants, which differ in terms of energy metabolism and nutritional requirements. After prolonged cultivation, the population in the binary culture contained only R cells (100%), which are characterized by minimum requirements with respect to the main biogenic elements. These data agree with the predictive data of model studies and can be attributed to regulation of the population composition of bacterial cultures by trophic factors. It was established that the proportion of M cells, which are distinguished by maximum nutrient requirements and enhanced stability, increased during two developmental stages of the Ps. aeruginosa polycultures (R + M and R + S + M): the lag phase and the decay stage. This result cannot be due to the influence of trophic factors and presumably results from changes in the levels of autoregulatory factors (anabiosis autoinducers) involved in stress resistance and plausibly in the adaptive interconversion of dissociants upon transfer to a new medium (during the lag phase) and under starvation conditions (at the onset of the decay phase).