This paper discusses the theory and experimental application of microcalorimetry to the study of solid state reactions of pharmaceutical importance. The practical example selected is that of formulated products containing benzoyl peroxide - a treatment for acne and athlete's foot. A newly developed procedure for data analysis is outlined and preliminary results from chemometric-based analysis of complex solid state reaction schemes is presented. Finally, the microcalorimetric requirements for such stability studies are contrasted with the newly emerging multi-channel "chip calorimeters" that operate in the nano range (watts, material, concentration) with high throughput potential. (C) 2004 Elsevier B.V. All rights reserved.