A comparative study on thermal behaviour of a commercial aminophylline (1) and three theophylline (th) compounds containing ethylenediamine (en) analogues, has been carried out by using simultaneous TG/DTA and evolved gas analysis (TG-FTIR). Theophylline ethylenediamine carbamate (2), 1,4-diammoniumbutane bis(theophyllinate) (3) and a physical mixture containing both 1,6-diaminohexane carbarnate and lattice compound of 1,6-diaminohexane with theophylline (4) have been prepared and heated to about 500 degreesC with 10 degreesC min(-1) rate. The thermal behaviour of the four samples has shown various similarities. Based on simultaneous TG/DTA curves and stoichiometric calculation, it can be seen that all the molecules of the solubilizers are released below 250 degreesC in flowing air atmosphere. The evolution rate of water of crystallization from aminophylline reaches a maximum at lower temperature than that of ethylenediamine, so water of crystallization leaves easier from the molecular compound. Ethylenediamme carbarnate is released as ethylenediamine and carbon dioxide in one TG step from compound 2 as observed by TG-FTIR. The coupled TG-FTIR analysis has also revealed that 1,4-diaminobutane is released without degradation from lattice 3. During the first step of decomposition of 4, the 1,6-diaminohexane carbamate evolved in form of carbon dioxide and diamine. In the second step. 1,6-diaminohexane is released from the targeted 1,6-diammoniumhexane bis(theophyllinate). In all cases, in the last step after a slight sublimation, the anhydrous theophylline melts and evaporates totally. (C) 2004 Elsevier B.V. All rights reserved.