To investigate the effect of size-excluded fraction of non-animal protein hydrolysate on growth, viability and longevity of Chinese hamster ovary (CHO) cells, several commercially available protein hydrolysates were evaluated as a feed supplement to chemically-defined protein-free suspension culture. Soy protein hydrolysates showed better supporting capability for cell growth and viability than the other types of hydrolysates. Maximal cell growth was not affected greatly by size exclusion of some soy hydrolysates such as bacto soytone and soy hydrolysates. CHO cells supplemented with size-excluded fractions of the two hydrolysates showed viable cell density and viability almost equal to those with their crude hydrolysates, although soy hydrolysates showed a little better performance. This suggested that the size-excluded hydrolysate fractions of some soy hydrolysate might be a potential culture medium additive to achieve better downstream operation in a large-scale production as well as enhanced productivity. (c) 2006 Elsevier Ltd. All rights reserved.