A recombinant Chinese hamster ovary (CHO) cell line producing human antithrombin III (ATIII) was cultured in serum-free medium to investigate the influence of temperature on metabolic activity and growth behavior. Cultivation below the physiologic temperature of 37 degrees C, in this case at 33 degrees C, lengthened the growth phase and reduced most consumption and production rates, excepting ATIII productivity, glutamine consumption, and ammonia accumulation. Thus, the use of a temperature shift (37 --> 33 degrees C) during the exponential phase is useful, because on the one hand, the maximal cell density was reached only 24-48 h later, and on the other hand, most cell metabolics were reduced at this point; therefore, process control can occur more easily, especially if a continuous process starts at this point.