The extreme toughness of spider silk is dependent on the silk's ability to dissipate most of the mechanical energy imparted to the fiber during loading processes through irreversible deformations. This basic property makes the tensile behavior of spider silk fibers depend on the silk's previous deformation history in a largely unpredictable way. The resulting variability often represents an insurmountable difficulty for both the characterization of the material and its practical usage. In this study, it was shown that spider silk is endowed with a property that allows to circumvent these problems: supercontraction, the large shrinkage of the longitudinal dimension of spider silk fibers in wet environments, recovers the tensile properties of deformed spider silk fibers in a repetitive and reproducible way. (C) 2004 Wiley Periodicals, Inc.