In a recent paper (1980) extending a preliminary study (1978) Chopin and Maluski, puzzled by the coexistence in a same geographic and structural area, of both Late Cretaceous (Eoalpine) and Late Eocene (Lepontine or Meso-Alpine) ages in white micas, deny the temperature control on the closure of K/Ar and ⁴⁰Ar/³⁹Ar isotopic systems of micas. These authors consider that the controlling factor would be diffusion enhanced by deformation, the chemical reactivity and initial mineralogy being secondary factors. This is an important question; unfortunately the presented data do not allow to answer it conclusively. We have been working for many years on Alpine radiometric dating, confronted every day with the fact that ever more numerous parameters and factors have to be considered. As we are harshly attacked in the interpretation of our radiometric data (Bocquet (Desmons) et al. 1974; Hunziker 1974; Delaloye and Desmons 1976) we feel entitled to comment on the validity of Chopin and Maluski's conclusions, on the quality of their experimental techniques, and to emphasize their incorrect and incoherent statements.