This study was initiated to test the biocompatibility, resorption and penetration characteristics of human collagen graft material in vitro and in vivo using light (LM) and electron microscopy (EM). To study this relationship, pieces of glutaraldehyde cross-linked collagen sponges (1 x 1 x 0.5 cm), were: (1) cultured in sterile Petri dishes with human gingival fibroblasts and human periodontal ligament fibroblasts for 2 weeks; (2) implanted in subcutaneous pockets made in both thighs (total 20 sites) of 10 Sprague-Dawley rats for 7-56 days. The behaviour of the growth of the fibroblasts was studied by inverted light microscopy (LM), then tissue culture specimens were studied from without and within using low-temperature scanning electron microscopy (LTSEM). Blocks obtained from the graft sites of the rat were processed for LM and transmission EM. Long-term LM observations showed attachment and random orientation of cells on and around the collagen sponge in culture during the first 48 h. Between 7 and 14 days, the majority of the cells adjacent to the sponge were orientated at right angles to its margin with their long axes approximately parallel to each other. The LTSEM revealed that large numbers of HGF and HPLF grew onto the collagen sponges, but no cellular penetration to the middle of the sponge was seen. LM and TEM of the rat specimens showed a cellular reaction to the collagen graft, as well as slow resorption, and fibroblast invasion of the graft at 6-8 weeks. It was concluded that the human collagen graft was biocompatible with HGF and HPLF, with penetration first observed at 42 days post-implantation. In the in vivo study, the collagen underwent slow resorption over a period of 8 weeks.