The rheological behavior of polyamide 11 samples with different initial moisture levels is investigated. More specifically, the time evolution of the linear viscoelastic properties is monitored at a given frequency. The time dependence of these properties is exponential in time, reflecting postcondensation reactions in the samples. The crossover time, at which the storage modulus and loss modulus intersect, can be used as a characteristic timescale for the reaction. This crossover time and the corresponding complex viscosity can be used as fingerprints of the material, reflecting the moisture content in the material. (c) 2005 Wiley Periodicals, Inc.