Artificial cross-shaped intrabony defects were created in the mandibles of 12 rabbits and the cavities covered with Type I highly cross-linked resorbable collagen membranes for 30 days. Similar cavities were prepared in three control animals and left uncovered for the same time period. Morphological and analytical data were obtained by means of light microscopy, scanning electron microscopy, and x-ray energy-dispersive spectrometry. After the experimental period, the membrane covered cavities were completely filled with regenerated bone. In the control specimens, the artificial cavities were occupied by fibrous connective tissue.