Viscometers have had a prominent role in the study of hydrodynamic damage to cell cultures. A Couette bioreactor overcomes stringent time limits of previous viscometric research. At low shear levels, the vessel supported robust growth of Spodoptera frugiperda cells (>92% viability) at 0.64+/- 0.09 day(-1) to a maximum cell density of 6.1 x 10(6) cells ml(-1). The intrinsic rate of necrosis was 30+ times slower than the specific growth rate. Cell death was bimodal, confirming recent reports of apoptosis in uninfected insect cells. Population dynamics suggests that early apoptotic cell formation accelerated 100-fold over a month, surpassing the rate of necrosis by day 4. Early apoptosis was the rate-limiting step in the apoptotic pathway and particularly sensitive to culture conditions. Accepted methods of estimating shear exposure were revised to account for the pseudoplasticity of Couette cultures: power-law parameters to = 0.660 +/- 0.054 dyne s(0.22) cm(-2) and n = 0.222 +/- 0.047. The maximum shear stress of 0.84 dynes cm(-2) was 70+ times the value predicted for a Newtonian fluid (1.0 cp viscosity). Prolonged shearing in a Couette bioreactor will enable investigation of cumulative stress effects and the shear response of cell processes with a long half-life.