This report describes the optimization of culture conditions for coenzyme Q(10) (CoQ(10)) production by Agrobacterium tumefaciens KCCM 10413, an identified high-CoQ(10)-producing strain (Kim et al., Korean patent. 10-0458818, 2002b). Among the conditions tested, the pH and the dissolved oxygen (DO) levels were the key factors affecting CoQ(10) production. When the pH and DO levels were controlled at 7.0 and 0-10%, respectively, a dry cell weight (DCW) of 48.4 g l(-1) and a CoQ(10) production of 320 mg l(-1) were obtained after 96 h of batch culture, corresponding to a specific CoQ(10) content of 6.61 mg g-DCW(-1). In a fed-batch culture of sucrose, the DCW, specific CoQ(10) content, and CoQ(10) production increased to 53.6 g l(-1), 8.54 mg g-DCW(-1), and 458 mg l(-1), respectively. CoQ(10) production was scaled up from a laboratory scale (5-l fermentor) to a pilot scale (300 l) and a plant scale (5,000 l) using the impeller tip velocity (V (tip)) as a scale-up parameter. CoQ(10) production at the laboratory scale was similar to those at the pilot and plant scales. This is the first report of pilot- and plant-scale productions of CoQ(10) in A. tumefaciens.