PM3 (RHF) type semiempirical quantum chemical calculations have been carried out on (nH(2) + Be)@C-120 Systems where C-120 is a capped tube and n less than or equal to 15. The results indicate that all these systems are stable but endothermic in nature. (7H(2) + Be)@C-120 system has the lowest heat of formation value. (C) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.