Devitrification studies are reported on NiFeSiB amorphous ribbons containing Ta. Differential scanning calorimetry (DSC) scans were performed at rates from 1 to 200 K/min. Two calorimetric peaks, partially overlapped, were found for Ni37Fe35Ta1Si10B17 at low scanning rates which merged into a single signal at high rates. Crystallisation produced always a mixture of phases. The glass transition, T-g, is manifest around 820 K in analyses at the highest scanning rate (200 K/min). A change in slope at 820 K occurred in the Kissinger plot of the second or single DSC signal. Two activation energies (E-a) were determined (509 kJ/mol and 302 kJ/mol for low and high temperatures respectively). These findings are interpreted as a confirmation of the occurrence of T-g. The Ni36Fe32Ta7Si8B17 ribbons showed a single transformation peak. Indication of T-g was never found in DSC. Two values of E, were obtained from the Kissinger plot (532 kJ/mol and 284 kJ/mol for low and high temperatures respectively). The values of E-a are discussed with reference to the mechanisms of atomic mobility below and above T-g.