Ion microscopy on fresh frozen cryostat sections, 5-10 mum thick, is useful to determine the distribution of elements and low molecular organic compounds in the larger areas of the tissues. Fresh frozen cryostat sections of tree frog eyeball were examined. Secondary ion images of Na, Mg, Al, C2H3, K, Ca and C3H5 were observed by ion microscopy (IMS-6f) using O-2(+) as the primary beam source at an energy of 15 keV. The primary beam current was 10(-10) A, the ion image magnification was varied from 300 to 1500 and the mass resolution was set between 300 and 3000. The areas of high intensity ion counts of the organic compounds generally showed low ion counts of elements. After long exposure to the primary ion beam, the intensity of the organic compound ions decreased, whereas the intensity of atomic ions of elements increased. (C) 2004 Elsevier B.V. All rights reserved.