Arginine is one of the universal reagents that are effective in assisting refolding of recombinant proteins from inclusion bodies. The mechanism of the effects of arginine on refolding has remained, however, to be elucidated. Here we show that arginine does not stabilize proteins against heat treatment, as demonstrated by little change in melting temperature. It does increase reversibility of thermal melting and reduce aggregation under thermal stress. The observations suggest that arginine may not facilitate refolding, but may suppress aggregation of the proteins during refolding. (C) 2003 Elsevier Science (USA). All rights reserved.