The drug acetazolamide (C4H6N4O3S2) was studied using a simultaneous thermogravimetric-differential thermal analysis (TG-DTA) unit. The study covered the temperature range of ambient to 600 degreesC. The DTA showed a melting point of 258.5 degreesC followed by a three-stage decomposition. The TG-DTG plots clearly show the decomposition when subjected to heat treatment in a nitrogen atmosphere. A kinetic analysis of all stages was attempted, where a zero-order process appeared to be the best fit mechanism and plots of In k versus T-1 show this. The values of E-act are shown to vary throughout each stage as the reaction progressed.