A new method for the preparation of porous polymer samples and investigations of their structure by scanning electron microscopy (SEM) is described. The technique for cleavage preparation is complemented by a preliminary treatment of a polymer with photo oxidation degradation to render it brittle. The advantages of this technique have been demonstrated with polyethylene tere-phthalate (PET) track membranes. The true size and shape of pores in the bulk sample can be seen in the cleavage plane. The degradation procedure does not change the membrane morphology. At the same time it allows one to reveal the characteristic features of the porous structure without its modification. Clear pictures of cross-sections of track membranes with cylindrical and bow-tie-like pore channels are presented. (C) 2003 Elsevier Science B.V. All rights reserved.