Summary We tested the hypothesis that a pressure difference can cause blebbing associated with uncoupling of the plasma membrane from the cortical actin, a phenomenon found earlier in locomoting blebbing Walker carcinosarcoma cells. Untreated, initially spherical Walker carcinosarcoma cells were exposed to suction pressure by partial aspiration into micropipettes. The suction pressure required to induce blebbing was in the range of 0.9 – 3 cm H 2O, i. e., somewhat lower than the increase in intracellular pressure measured before formation of protrusions in Amoeba proteus (Yanai et al., Cell Motil. Cytoskeleton 33, 22 – 29, 1996). The response was temperature-dependent, blebbing occurring more frequently at 37 °C than at room temperature. Blebbing was associated with formation of cytoplasmic actin layers, restriction rings and/or of gaps in the plasma membrane-associated cortical actin. The results support the view that blebbing associated with uncoupling of cortical actin and plasma membrane as observed in locomoting cells can be caused by a pressure gradient.