Uncaria tomentosa cell suspension cultures were grown in a 2-L stirred tank bioreactor operating at a shear rate, (gamma) over dot(avg) = 86 s(-1) The cultures showed an early monophasic oxidative burst measured as H2O2 production (2.15 mu mol H2O2 g(-1) dw). This response was followed by a transient production of monoterpenoid oxindole alkaloids (178 +/- 40 mu g L-1 at 24 h). At the stationary phase (144 h), the increase of the shear rate (gamma) over dot(avg) up to 150 s(-1) and/or oxygen tension up to 85% generated H2O2, restoring oxindole alkaloid production. U. tomentosa cells cultured in Erlenmeyer flasks also exhibited the monophasic oxidative burst but the H2O2 production was 16-fold lower and the alkaloids were not detected. These cells exposed to H2O2 generated in situ produced oxindole alkaloids reaching a maximum of 234 +/- 40 mu g L-1. A positive correlation was observed between the oxindole alkaloid production and the endogenous H2O2 level. On the other hand, addition of 1 mu M diphenyleneiodonium (NAD(P)H oxidase inhibitor) or 10 mu M sodium azide (peroxidases inhibitor) reduced both H2O2 production and oxindole alkaloids build up, suggesting that these enzymes might play a role in the oxidative burst induced by the hydrodynamic stress.