Denaturation of fructose-1,6-bisphosphatase (Fru-P2-ase, EC 3.1.3.11) by urea and renaturation of denatured enzyme has been investigated. Denaturation lowers the specific activity of the enzyme but even at 8 M urea concentration in the presence of sucrose the activity of the enzyme is detectable. Centrifugation of the enzyme in a sucrose density gradient at 4 M urea reveals one peak of protein corresponding to a dimer. Denaturation increases intensity of intrinsic fluorescence of Fru-P2-ase and causes a red shift of fluorescence peak of the thioisoindole derivative of the enzyme. Renaturation of the denatured enzyme followed as the reappearance of enzymatic activity in the presence and absence of bovine serum albumin (BSA) is characterised by first order kinetics, k = 1.78 X 10(-3) s-1. The presence of BSA does not affect the rate of renaturation but perceptibly increases the recovery of enzymatic activity. A 100% recovery of Fru-P2-ase activity is observed at 0.5 micrograms/mL concentration of the enzyme and 2 mg/mL of BSA.