In the resting position and in persons with normal jaw relations the lips have a mutual surface of contact. Clinically, the area of contact constitutes a well-defined zone. This contact zone was made visible by smearing with ointment and measured in 24 young and 21 older persons. In all subjects the contact zone was band-shaped. Its widest dimension occurred laterally, narrowing medially. In the corner of the mouth it measured approx. 7.0 mm on an average, and in the median plane approx. 3.5 mm. A comparison was made of the changes that occur in the pars intermedia and the contact zone with advancing age. In the older subjects a significant reduction was recorded in the width of the pars intermedia (approx. 40 %). The dimensions of the contact zone on the other hand altered only slightly with age. The function of the contact zone is probably to seal the oral fissure when the mouth is closed. Surface contact between the two lips ensures effective adhesion.