Collagen films were prepared by three different methods involving acid homogenization at pH 3.0 of a collagen suspension for 1.5 min (film A) and 15 min (film B) and alkaline homogenization at pH 10 for 15 min (film C), after which the resulting slurries were degassed and dried over sterile air. Subsequent examination by scanning electron microscope (SEM) revealed that all samples showed a distinctly layered structure which was much finer in the acid films. Implantation into the lumbar muscle of rats followed by histology and SEM studies revealed that film B was completely resorbed at 14 d whereas remnants of film A could still be seen at this period. The slowest rate of resorption was observed with film C, traces of which could still be found at 70 d. Invading inflammatory cells moved into the collagen films between the layers from the edges only causing the whole structure to 'ribbon out'. The surfaces of all three films appeared to be impenetrable to cells. Incubation of the three films with bacterial collagenase revealed similar relative rates of degradation to those observed in vivo.