In a previous study by our group (Ripoll et al. (1993), C.R. Acad. Sci. Paris, 316, 1438-1445), it was observed that the value of the Na/Ca concentration ratio was much larger in the cells with differentiated secondary walls (e.g. fibres in flax plants, or xylem of woody dicotyledons) than it was in the other cells. In the present contribution we study the relative distributions of Na, Mg and Ca in the various cell types (meristem, phloem and xylem) of the cambial area of 1 to 2 years old branches of beech trees (Fagus sylvatica L.).Beech branches were sampled i) at the end of January (quiescent cambium) ii) at the end of March (cambium preactivation) and iii) at the end of April (cambium activity). Small pieces of cambial tissue were prepared using the pyroantimonate precipitation technique (Mentre and Escaig (1998), J. Histochem. Cytochem., 36, 48-54). The ionic distributions were imaged using scanning Secondary Ion Microscopy and Spectrometry (CAMECA IMS4f, Courbevoie, France).The ionic concentrations in the phloem and the xylem normalized to that in the cambium show a general tendency to increase from January to March then April, with the exception of the normalized xylem Ca and Na concentrations which exhibit a clear minimum in March. There is thus a specific and transient modification of the ionic status in the cambial area at the moment when cambium preactivation takes place.