For experimental investigations in the field of microdosimetry of heavy ions a high precision localization method for biological objects relative to the path of the penetrating ion is mandatory. New methods are described for corn seeds ofArabidopsis thalianaand spores ofBacillus subtilis.In the latter case the actual penetration point of the particle in the spore layer is determined by an individual microetching technique with an accuracy of about 0.2 μm. This is done after removing the spores from the hit area by “break-through” etching. With the help of reference spores the impact parameter is determined for correlating the biological effects with the physical event. Besides the aspect of water during the track development is described.