The potential bioactivity of eight distinct casein hydrolysates (designated a-h) was assessed by investigating different parameters on human cultured cells. Following 24 h supplementation, the casein hydrolysates exerted varying effects on the viability and growth of Jurkat T cells, with IC50 values ranging from 19.5% to 66.8% (v/v). Treatment with the hydrolysates did not affect the membrane integrity or superoxide dismutase activity of Jurkat cells. Sample a significantly affected both cellular catalase activity and reduced glutathione (GSH) content, whereas samples c, cl, and e enhanced (P < 0.05) GSH content. Neither genotoxic nor genoprotective effects were exerted by the casein hydrolysates. Interestingly, the casein hydrolysates d-h significantly increased Concanavalin A (ConA)-stimulated IL-2 levels but had no effect on ConA-induced IL-10 production in the Jurkat cells. The differing bioactive effects of these casein hydrolysates may, in part, be attributed to differences in the enzyme specificities of the enzyme activities used in their preparation. (c) 2009 Elsevier Ltd. All rights reserved..