Serum-free perfusion cultures of hybridoma TO-405 cells were carried out in spinner flasks coupled with zeolite A-3 packed beads. Ammonia was selectively removed from the culture broth by passing cell free permeate from ceramic cross flow filtration, through the zeolite packed bed. Ammonia concentration in the culture broth was effectively maintained between 1 to 4 mmol/l which was below the inhibitory concentration for cell growth. Maximum cell density levels of 10(7) cells/ml as well as improved percentage cell viability higher than in serum-supplemented cultures were feasible in this system. The possible effects of shear stress, generated by variation of the flow rates of the broth through the ceramic filter module, on the growth of the hybridoma cells were investigated. Backwashing, by reversing the direction of the permeate, was found necessary to prolong the life of the filter. Variation of the flow rates of the broth through the ceramic module between 0.29 m/s to 0.59 m/s did not cause immediate cell damage but growth was repressed at the higher flow rate. This study also showed that glutamine appears to be one of the factors limiting the growth of the hybridoma cells.