In this study a pulse nuclear magnetic resonance H-1 NMR technique was used to determine the relaxation time (T-2) from Carr-Purcell-Meiboom-Gill (CPMG) experiments on fillets of Pintado (Pseudoplatystoma corruscans) at -70 to 60 degreesC and in the freeze-dried fillets, reconstituted to a moisture content of 1-32%, at 10, 25 and 40 degreesC. Analysis of data obtained from CPMG experiments using the MARAN WinDXP software resulted in T-2 spectra. Profiles of water fractions with different mobility have been obtained, and glass transition values have been determined. These profiles were affected by environment conditions, such as temperature, moisture and water activity. We compared the water activity method with NMR technique in measuring water molecular mobility. The NMR technique proved that it is an alternative tool to better understand water behavior in complex biological systems. (C) 2002 Elsevier Science Ltd. All rights reserved.