Using Secondary Ion Microscopy and Spectrometry (SIMS), we have studied the distribution of K + , Na + , Mg 2 + and Ca 2 + cations in pollen grains of white birch (Betula verrucosa Ehrh.). To prevent ion loss during fixation, dehydration and embedding treatments, we developed a new preparation method (Verdus M.C. et al., in preparation.). Fixation and dehydration were performed respectively in acrolein vapour and dimethoxy-2,2-propane vapour acidified with HCl. This method prevented the contact of the pollen grains with aqueous solutions at each step of the sample preparation. Moreover the contact with liquids was limited to that with the resin and solvent mixtures required for embedding. Transmission electron microscopy showed that our preparation method allowed a very good preservation of pollen ultra-structures and, in addition, a good retention of water soluble allergens. Scanning SIMS images of K + , Na + , Mg 2 + and Ca 2 + distributions in pollen grains from different batches obtained using this method were highly reproducible. We observed that monovalent cations were mainly concentrated in spots which could correspond to starch grains whereas divalent cations were mainly found near apertures and in the sperm cell. We also performed an Energy Dispersive X-ray microanalysis (EDX) study on pollen grains from the same batches as those used for the SIMS study. We then compared our results to those previously obtained by other authors (Cerceau-Larrival M.T. et al. (1994), JTMT, 12, 37-50) and found that EDX was a simple technique to obtain the mean ion concentration in the whole pollen grain, whereas SIMS revealed to be a very sensitive technique for the imaging of the local ion distribution.