A study of martensitic and premartensitic transitions in a Ni-Mn-Ga alloy with near stoichiometric composition is reported. We present results from acoustic emission detected during both transitions. Results are complemented with calorimetric and magnetic susceptibility measurements. The effect of thermal fluctuations in both transitions has also been examined. Results suggest that the premartensitic transition has an athermal character whereas the martensitic transition exhibits thermally activated effects. Results for the amplitude distribution of acoustic emission pulses have been obtained for both transitions. No significant differences were found between the exponents corresponding to each transition. (C) 2004 Elsevier B.V. All rights reserved.