Effects of culture temperature ranging from 20 to WC on cell growth, polysaccharide biosynthesis and the bioactivity of polysaccharides of Agaricus blazei were evaluated via eight batch cultures in steps of 2 degrees C in a stirred tank bioreactor. Results indicated that the optimal temperature for the biomass was 28 degrees C with a cell yield of 780 mg g(-1), while that for polysaccharide formation was 30 degrees C with a product yield of 230 mg g(-1). Both the P-glucan content and average molecular weight of the polysaccharides from different temperature-controlled cultures were closely correlated with their tumour necrosis factor-a (TNF-alpha) release capability on macrophage cells. The polysaccharides from the low temperature range (20-24 degrees C) not only had higher relative content of beta-glucan and average molecular weight but also exhibited higher bioactivity compared with those from the high temperature range (30-34 degrees C). The optimal temperature for the production of bioactive polysaccharides of A. blazei was 24 degrees C, at which their relatively high molecular weight, beta-glucan content and TNF-alpha release capability on macrophage cells were 1650 kDa, 188 mg g(-1) and 1560 pg per 5 x 10(4) cells respectively. (C) 2007 Society of Chemical Industry.