We present evidence of time stretching in the peak-to-peak time scales in the light curves of BATSE gamma-ray bursts (GRBs). Extensive tests are performed on simulated samples of artificially dilated bursts to verify that the procedure for extracting the peak-to-peak intervals correctly recovers the input stretching of bursts. The resulting robust algorithm is then applied to the 4B GRB database. We derive a factor of 1.92±0.13 stretching between the bright burst group (P>7.7 photons cm−2 s−1) and the dimmest burst group (P=1.0−1.4 photons cm−2 s−1), which is a 7 σ effect. This measurement strongly supports the interpretation of the observed time stretching as time dilation caused by the universal cosmological expansion. In the standard candle scenario, this result implies that the burst luminosity is 7.0−2.0+2.0×1056photons s−1, which suggests that the brightest bursts are at redshift of zbright<0.2.

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