Production of recombinant proteins in plants through Agrobacterium-mediated transient expression is a promising method of producing human therapeutic proteins, vaccines, and commercial enzymes. This process has been shown to be viable at a large scale and involves growing large quantities of wild-type plants and infiltrating the leaf tissue with a suspension of Agrobacterium tumefaciens bearing the genes of interest. This study examined one of the steps in this process that had not yet been optimized: the scale-up of Agrobacterium production to sufficient volumes for large-scale plant infiltration. Production of Agrobacterium strain C58C1 pTFS40 was scaled up from shake flasks (50-100 mL) to benchtop (5 L) scale with three types of media: Lysogeny broth (LB), yeast extract peptone (YEP) media, and a sucrose-based defined media. The maximum specific growth rate (mu (max)) of the strain in the three types of media was 0.46 +/- 0.04 h(-1) in LB media, 0.43 +/- 0.03 h(-1) in YEP media, and 0.27 +/- 0.01 h(-1) in defined media. The maximum biomass concentration reached at this scale was 2.0 +/- 0.1, 2.8 +/- 0.1, and 2.6 +/- 0.1 g dry cell weight (DCW)/L for the three media types. Production was successfully scaled up to a 100-L working volume reactor with YEP media, using k (L) a as the scale-up parameter.