The biology underlying normal and premature cranial suture fusion remains unknown. The purpose of this study was to investigate the role of the dura mater in cranial suture fusion. In the Sprague Dawley rat model, the posterior frontal cranial suture fuses between 10 and 20 days of postnatal life. The effect of separating the posterior frontal cranial suture from its underlying dura mater with an intervening silastic sheet was studied. Sixty rat pups, age 8 days, were divided into four groups of 15. Group A served as unoperated controls. Group B, the experimental group, underwent craniotomy, dural elevation, and insertion of a silicone sheet between the posterior frontal cranial suture and the underlying dura. Two operative sham groups were included. Group C underwent craniotomy and dural deflection only. Group D underwent craniotomy alone without dural deflection. The rats were sacrificed at 15, 22, and 30 days of age. The results showed that the unoperated animals (group A) demonstrated normal initiation of suture fusion at 15 days and complete fusion by 22 days. Group B animals, with silicone sheet barriers placed, showed persistent patency of sutures at 22 days. Initiation of suture fusion was delayed until 30 days. Sham group C, animals with craniotomy and dural deflection, showed that initiation of fusion was delayed until 22 days with complete fusion by 30 days of age. Sham group D, craniotomy alone, had the same normal temporal sequence of suture fusion as the unoperated control group A. These data indicate that normal cranial suture fusion is delayed when the suture-dural interaction is interrupted by a surgically place barrier or by simple dural deflection. Furthermore, interaction between the dura and the overlying suture appears to direct suture fusion.