Some photocromic compounds involve photoinduced intramolecular proton transfer (PIPT) as a consequence of a fast electronic redistribution due to electronic excitation. In this study, we have examined the PIPT that occurs in 2-(2'-hydroxyphenyl)-4-methyloxazole (HPMO) in gas phase and encapsulated in beta-cyclodextrin (beta-CD). An hybrid method has been employed for electronic calculations of the confined geometry. Even though our results indicate that there is no significant difference between the PIPT process of HPMO in gas phase and encapsulated in beta-CD, we also show that the effect of the confinement on the intramolecular proton transfer is not negligible. (C) 2002 Published by Elsevier Science B.V.