A scanning electron microscope (S.E.M.) was used to examine dentinal tubules transversely fractured approximately 1.5 mms below a superficial dentinal attritional surface. The material not only included vital teeth but also young, intact premolars implanted into removable dentures. In these teeth the enamel on the buccal cusps was removed and the dentine exposed to attrition for 3 years. For comparison the tubules of intact teeth transversely fractured at the same level were examined. Intact control revealed open tubules of normal size in the area examined. Under attrited surfaces many tubules on the same level were completely occluded with material similar to that seen in peri-tubular dentine. Other tubules had varying degrees of reduction of the tubule lumen. The situation was the same in 4 teeth attrited in removable dentures. The findings support the view that while tubules in sclerotic dentine in teeth subjected to attrition may be occluded by a continuous growth of peritubular dentine, the oral milieu and saliva may also contribute to this process.