Embryogenic cultures of a transformed Eschscholtzia californica cell line were carried out in a 11-L helical ribbon impeller bioreactor operated under various conditions to evaluate the performance of this equipment for somatic embryo (SE) production. All bioreactor cultures produced SE suspensions with maximum concentrations at least comparable to those obtained from flask control cultures (similar to 8-13 SE.mL(-1)). However, an increase of the mixing speed, from 60 to 100 rpm, and low sparging rate (similar to 0.05 VVM, k(L)a similar to 6.1 h(-1))for dissolved oxygen concentration (DO) control yielded poorer quality embryogenic cultures. The negative effects on SE production were attributed mainly to the low but excessive shear experienced by the embryogenic cells and/or embryo-forming aggregates. High DO (similar to 60% of air saturation) conditions favored undifferentrated biomass production and high nutrient uptake rates at the expense of the slower SE differentiation process in both flask and bioreactor cultures. Too low DO (similar to 5-10%) inhibited biomass and SE production. The best production of SE (similar to 44 SE.mL(-1) or similar to 757 SE.g dw(-1).d(-1))was achieved by operating the bioreactor at 60 rpm while controlling DO at similar to 20% by surface oxygenation only (0.05 VVM, k(L)a similar to 1.4 h(-1)). This production was found to be a biomass production/g rowth-associated process and was mainly limited by the availability of extracellular phosphate, magnesium, nitrogen salts, and carbohydrates.