This study was an attempt to investigate whether there was any oxytalan fibre increase in the transseptal region as a result of orthodontic movement, and if so, whether this could be a contributory factor in the problem of relapse. The experimental model was based on orthodontic movement of maxillary molars in rats, followed by a light microscopic examination and registration of the oxytalan fibres in two different areas of the periodontium as well as within the transseptal fibre region. Within the transseptal fibre bundles there was no increase in the oxytalan fibre concentration, although in the periodontal ligament deep to the transseptal fibres a slight increase had occurred. The oxytalan fibres that were seen were nearly always in close proximity to blood vessels. Oxytalan fibres seem to play little if any role in relapse of orthodontic movement.