Fungal pathogens which cause seedling disease complex (SDC) in cotton (Gossypium spp.) preferentially infect plants which are environmentally stressed, further inhibiting growth of plants already weakened by non-optimal growing conditions, e.g., suboptimal spring soil temperatures.Seedlings of C. hirsutum, var. Paymaster 145, were grown at 10, 15, 20, 25, 30, or 35 C from Day 2 through Day 13 in sterile soil or in SDC-infected soil which contained 0, 1, 2, or 4 gin/75 cm³ of a commercial formulation of an SDC biocontrol agent, containing Pseudomonas fluorescens strains [Dagger G(TM)]. The final cotyledon areas, root and shoot lengths, fresh weights, dry weights, and relative water contents were determined and compared to the analogous values from seedlings grown at 30 C in sterile soil (controls). Growth in non-sterile soil at 10 and 15 C significantly decreased root and shoot elongation, root and shoot fresh weight accumulation, root dry weight gain, and cotyledon expansion. The SDC biocontrol had no effect on the inhibition at these temperatures. The presence of the biocontrol agent increased the inhibition of root dry weight accumulation in seedlings grown in non-sterile soil at 20 through 30 C. When seedlings were grown at 25 through 35 C in non-sterile soil, the biocontrol agent promoted root elongation and accumulation of shoot fresh and dry weight. Overall, seedling responses to these isothermal temperature treatments were more important than the responses to biocontrol concentration. If seedlings were grown in non-sterile soil at 10, 15, 20, 25, or 35 C from Day 3 through Day 11 and then placed in an optimal 30 C environment on Day 12 through Day 13, cotyledon expansion was increased in those seedlings exposed to the biocontrol agent at 15, 20, 25, and 35 C. Growth-promotive biocontrol agent activity (2 or 4 gram treatment) was most apparent in those seedlings which were allowed to recover for 48 hours at 30 C after exposure to a non-optimal temperature. Relative water contents of roots and shoots were least affected by non-sterile soil and the presence of the biocontrol product.