In a previous study, we speculated that shear stress might enhance the renin productivity of recombinant Chinese hamster ovary (rCHO) cells cultivated in a radial-flow reactor (Motobu er al., J. Ferment. Bioeng., 83, 443-450, 1997). In order to clarify the effect of shear stress on cell function, we designed a sheer stress apparatus and investigated the cell morphology, cell cycle, renin productivity, and mRNA expression. In the case of subconfluent cells, which were mostly observed in the radial-flow reactor, it was found that after 24 h of shear stress exposure at 0.02 and 0.082 N/m(2), the cell morphology became longer and slimmer, and cell growth in the subconfluent monolayer was inhibited as compared to that in a static culture. The results also showed that the cells were arrested in the G(0)/G(1) phase of the cell cycle. However, renin productivity was found not to change under shear stress at 0.02 and 0.082 N/m(2) within 24 h, although the expression of renin mRNA under the shear stress condition was increased. With regard to confluent cells, it was surprising to find that shear stress did not influence the cell growth, cell cycle, renin productivity, or expression of mRNA within 24 h. Shear stress thus appears to affect subconfluent cells rather than confluent ones.