Centaurea calcitrapa suspension cultures were grown either in Erlenmeyer. asks or in a mechanically stirred bioreactor. Its rheological behaviour, when fitted to the Oswald - de Waele model ( power law), showed pseudoplastic characteristics in both cases. The flow behaviour index (n) decreased over the course of a growth cycle and the consistency index (K) increased, reached a value of 1.81 N s(n) m(-2) run on 2 l bioreactor. Bioreactor cultivation of C. calcitrapa cells at different agitation rates ( 30, 60, 100 and 250 rpm), highlighted the influence of shear forces on cell viability loss ( 90 -34%) and phenol accumulation ( 74 - 140 mu g l(-1)), due to increased stirring speeds. Analysis of these results suggests that this cell line is shear-sensitive. An empirical exponential correlation was defined between apparent viscosity and biomass concentration, under the studied conditions, giving the possibility to estimate the prevailing broth regime and to optimize bioreactor design.