Large-scale transient gene expression (TGE) in mammalian cells is a rapid method to generate recombinant proteins, but the volumetric productivity for secreted proteins is still more than an order of magnitude lower than the yields typically achieved with recombinant cell lines. Here transient recombinant protein production in Chinese hamster ovary cells transfected with linear 25 kDa polyethylenimine was significantly enhanced by incubation of the cells at temperatures ranging from 29 to 33 degrees C after DNA delivery. With this approach, transient recombinant antibody yields of 60-80 mg/L were achieved within 6 days of transfection. The increase in TGE correlated with the accumulation of cells in the G1 phase of the cell cycle, increased cell size, higher cell viability, higher steady-state levels of transgene mRNA, reduced consumption of nutrients, and decreased accumulation of waste products. The enhancement of TGE was not vector-dependent, but the presence of the woodchuck hepatitis virus post-transcriptional regulatory element in the 3' untranslated region of the transgene mRNA increased transient recombinant antibody expression more than 3-fold at 31 degrees C as compared to expression at 37 degrees C. The yields achieved by the low-temperature enhancement of TGE in CHO cells makes this technology feasible for the rapid production of gram amounts of secreted recombinant proteins at large scale (up to 100 L).