Rabbit muscle aldolase, which exists in solution as essentially globular, compact, highly organized particles of molecular weight 1.42 X 106, was readily dissociated into three polypeptide chains apparently without the rupture of covalent bonds. This dissociation was effected by treatment with any of the reagents, urea, HC1, acetic acid, or sodium dodecyl sulfate. Detailed studies of the subunits generated in 4 m urea solutions at pH 5.5 and in acid solutions (pH 2) showed that the polypeptide chains were markedly disorganized as coil-like particles of weight-average molecular weight 0.46 X 105. Upon dissociation and denaturation the reduced viscosity increased from 4.0 ml/g for the native enzyme to 23 ml/g at pH 2 and 18 ml/g in 4 m urea solutions. The optical rotation, [a]d, changed from -23°for the native protein to -62°and -83°for the aciddissociated and urea-dissociated subunits respectively. Similarly there was a marked change in the Drude constant, Ac, from 283 mp to 238 mp and 223 m^i. Accompanying the change in the conformation of the polypeptide chains was a blue shift in the absorption spectrum with AmaI decreasing from 279.7 mp for the native protein to 277.0 mp for the subunits. Analyses of the shift by difference spectra revealed contributions from chromophoric groups of tyrosine, tryptophan, and phenylalanine due to the altered environment of these chromophores in the dissociated chains as compared to the intact enzyme. Titration of the sulfhydryl groups showed that the 16 groups which are "masked" in the native enzyme reacted readily in the dissociated subunits.No enzymic activity could be detected in the subunits in the presence of urea. However, activity was regained with yields of 65% when the dissociating agents (hydrogen ions or urea) were removed by dilution or dialysis. Reconstitution experiments were performed under different conditions; pH 5.5 and concentrations greater than about 50 /il/ml were found to be optimal for the restoration of activity. Kinetic studies showed that extensive annealing was unnecessary, for enzymic activity was regained in only a few minutes. The reconstituted protein was characterized by its reduced viscosity, sedimentation coefficient, molecular weight, optical rotatory dispersion, absorption spectrum, titratable sulfhydryl groups, and specific activity. In all respects the reconstituted macromolecules were virtually identical to the native enzyme.