To maximize the production of flag-tagged cartilage oligomeric matrix protein angiopoietin-1 (FCA1) from Chinese hamster ovary (CHO) cells, the effects of culture pH and temperature on cell growth and FCA1 production were investigated. Cells were cultivated in a bioreactor at different culture pH (6.7, 6.9, 7.2, and 7.5) and temperatures (33 and 37 A degrees C). Lowering the culture temperature suppressed cell growth while allowing maintenance of high cell viability for a longer culture period. The specific FCA1 productivity (q (FCA1)) was increased at low culture temperature. Accordingly, the highest FCA1 concentration was obtained at pH 7.2 and 33 A degrees C, and was approximately 4.0-fold higher than that at pH 7.2 and 37 A degrees C. However, aggregates and a monomeric form of FCA1, which are undesirable due to reduced biological activity or immunogenicity, were significant at pH 7.2 and 33 A degrees C. It was also found that the expression pattern of FCA1 was affected more significantly by culture pH than by the culture temperature. FCA1 aggregation dramatically decreased at culture pH 7.5 regardless of the culture temperature. Furthermore, the monomeric form of FCA1 was not observed. Taken together, optimization of culture temperature and culture pH (33 A degrees C and pH 7.5) significantly improves the production of biologically active FCA1 with tetrameric or pentameric forms from CHO cells.