The entomopathogenic fungus Metarhizium robertsii is a common inhabitant of soils worldwide, being particularly abundant in the rhizosphere. The germination rates of 11 fungal entomopathogens (genera Metarhizium and Beauveria) and 2 other fungi (the rhizosphere-competent Trichoderma harzianum and the nonrhizospheric Aspergillus niger) were evaluated at 1, 2.5, 5, 10, and 20 mg/ml of bean root exudates (RE). Broad host range Metarhizium strains were as good at germinating in RE as T. harzianum but germination rates of narrow host range Metarhizium acridum 324 and Beauveria bassiana strains were significantly lower. At RE concentrations <1 mg/ml, M. robertsii ARSEF 2575 showed higher germination rates than T. harzianum. Time-course microarray analyses identified 50/1748 (2.9%) M. robertsii genes that were differentially expressed while growing in 5 mg/ml of RE. Up-regulation of genes (29/50, 58%) occurred mainly 4 and 8 h postinoculation with fold increases between 0.8 and 3.7. Up-regulated genes included the subtilisin Pr1A and the MAD2 (Metarhizium adhesin-like protein 2), which is responsible for attachment to plant surfaces. Other up-regulated genes were in the functional groups of carbohydrate, lipid and energy metabolism, extracellular matrix/cell wall proteins, transport proteins, DNA synthesis, sexual cycle, and stress response. A large number of hypotheticals/orphan proteins (41.3%) were also up-regulated indicating that many previously uncharacterized genes may have functions related to saprophytic survival. Knowledge of M. robertsii genes involved in adaptation to soil environments, particularly at early time points, is important when considering the potential commercial use of this biological control agent.