Macroporous microcarriers such as Cytopore entrap mammalian cells in a mesh network allowing growth to high cell concentrations in a protected environment within a stirred culture. Chinese hamster ovary (CHO) cells producing recombinant human β-interferon (IFN-β) and grown in Cytopore microcarriers showed a 2.6- to 2.8-fold increase in the volumetric product titer compared with cells grown in an equivalent suspension culture. In an attempt to maximize production of IFN-β, microcarrier cultures were subjected to a low temperature regime. Low temperature culture conditions (32°C) have been shown previously to enhance cell specific productivity in suspension cultures although at reduced cell growth rates. These conditions can be optimized by a timely shift from physiological to hypothermic conditions during the culture run to maximize volumetric protein production. In the case of IFN-β production the lower temperature has the added advantage of stabilizing the product and reducing intramolecular aggregation. Using a biphasic temperature-shift regime from 37 to 32°C the volumetric production of IFN-β was enhanced to 4.2-fold compared with a single temperature suspension culture in a controlled bench-top bioreactor. Furthermore, the degree of intramolecular aggregation of IFN-β was reduced significantly (59%) compared with control cultures, largely due to the lower temperature but also partially due to the presence of microcarriers. These results indicate that the hypothermic conditions in a Cytopore culture had a combined and possibly synergistic effect of increasing volumetric production of the recombinant protein.