Relative concentrations of four isomers of Ca@C-72 (one species with isolated pentagons, two isomers with a pentagon-pentagon junction, one structure with a heptagon) are computed using the Gibbs energy in a broad temperature interval. It is shown that both isomers with pentagon-pentagon junction are relatively close in concentrations at higher temperatures while the structure with isolated pentagons comes as a minor isomer (though it is the highest in potential energy) and the structure with heptagon is always negligible. (C) 2003 Elsevier Science B.V. All rights reserved.