The role of extracellular protease production by the fluorescent Pseudomonas strain M114 in the colonization of sugarbeet roots and non-rhizosphere soil was investigated. In sterile soil, a protease-negative mutant, M114-Prt-, exhibited superior persistence during 16 days on sugarbeet roots compared to the protease positive strain, M114-Prt+ (P = 0.015). On sugarbeet roots grown in unsterile soil, there was no difference in the survival of M114-Prt- compared to M114-Prt+ during 48 days. In sterile non-rhizosphere soil, M114-Prt- maintained higher cell numbers than M114-Prt+ during 150 days (P = 0.001). In unsterile non-rhizosphere soil, the colonization patterns of the two strains were not significantly different. These results show that extracellular protease production is not an important trait required by strain M114 to survive on sugarbeet roots or in non-rhizosphere soil.