A thermosensitive wild-type strain (PP201) of Rhizobium sp. (Cajanus) and its 14 heat-resistant mutants were characterized biochemically with regard to their cell surface (exopolysaccharides (EPSs) and lipopolysaccharides (LPSs)) properties and protein profile. Differences were observed between the parent strain and the mutants in all these parameters under high temperature conditions. At normal temperature (30 degrees C), only half of the mutant strains produced higher amounts of EPSs than the parent strain, but at 43 degrees C, all the mutants produced higher quantities of EPS. The LPS electrophoretic pattern of the parent strain PP201 and the heat-resistant mutants was almost identical at 30 degrees C. At 43 degrees C, the parent strain did not produce LPS but the mutants produced both kinds of LPSs. The protein electrophoretic pattern showed that the parent strain PP201 formed very few proteins at high temperature, whereas the mutants formed additional new proteins. A heat shock protein (Hsp) of 63-74 kDa was overproduced in all mutant strains.