Addition reaction of an endohedral metallofullerene La@C-82 with digermirane has been investigated by means of the mass and EPR measurements. It is found that photochemical and thermal reactions of La@C-82 with digermirane afford an exohedral adduct of the endohedral metallofullerene. This is in sharp contrast with the fact that empty fullerenes react only photochemically. The remarkable thermal reactivity of La@C-82 is ascribed to the unique electronic properties due to endohedral metal doping. (C) 1996 Elsevier Science Ltd