Polysaccharopeptide (PSP) derives from the medicinal mushroom Coriolus versicolor is considered a biological response modifier with potential pharmaceutical applications. Significant literatures support the immune and anticancer functions of PSP; however, standardization is of big concern because variable biotechnological factors can affect both the chemical and biological properties of PSP. In this study, the extracts of PSP obtained at different days from the Coriolus versicolor culture were tested in vitro for their immune function on human normal peripheral blood mononuclear cells (PBMC) and cytotoxicity on the human leukemia Molt 4 cells. Over the 10-days culture period, both biomass and peptide/polysaccharide content were increased with time. The increase in proliferation index of PBMC and their production of interleukin I beta (IL-I beta), tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) in the presence of PHA strengthens the correlation between culture duration and biological potency of PSP. The growth inhibition of the Molt 4 cells by PSP also depended on its maturity. Flow cytometry analysis on cell cycle and cell death (apoptosis) of Molt 4 cells indicated that the anticancer mechanism of PSP is related to its ability to induce S-phase cell arrest and apoptosis, respectively. To-ether, these results suggest that monitor the harvest duration is critical for the quality control of polysaccharopeptide in the biotechnological industry. (c) 2005 Elsevier Inc. All rights reserved.