Experiments were conducted on immobilized aggregates of Escherichia coli cells. Mechanical stress was applied by forcing a convective stream of nutrient medium through the aggregate. It was shown to be possible to maintain uniform exponential growth with this convective supply of nutrients. Analysis of effluent from the system allowed investigation of metabolic responses unambiguously attributable to mechanical stress. A reversible increase in catabolic activity was observed after an increase in mechanical stress. Changes in the level of catabolism were accompanied by an alteration in the total acid yield on glucose and in the spectrum of organic acids produced during glucose fermentation. The behavior observed here was likely due to an osmoregulatory response induced by the mechanically stressed bacteria to counteract changes in shape.