In the search for a new synthetic substitute for the dura mater, the authors conducted a research study using 32 mongrel dogs divided into three groups. Group I animals (21 dogs) underwent a right-sided parietooccipital craniotomy and substitution of two 1-cm pieces of dura mater by two different grafts: one piece of biosynthetic cellulose (50 mu thick) and one fragment of temporal fascia. The animals were observed for 30, 90, or 180 days. Group II animals (five dogs) underwent a somewhat larger craniotomy, removal of a 2-cm piece of dura mater, and lesioning of the cortex made by a thin sharp forceps, which caused bleeding that was controlled by application of a thin film of cellulose (10 mu thick). Duraplasty was performed using a 50-mu-thick cellulose membrane to complete the procedure and the animals were observed over a period of 270 days. Group III animals (six dogs) underwent smaller (1-cm diameter) bilateral parietal craniectomy, which included additional covering of the dura on the left side with 50-mu-thick cellulose and a suture of temporalis muscle. This group was observed for 40, 60, 80, or 120 days. Transient mild clinical symptoms were observed during the early postoperative period. At autopsy, macroscopic examination demonstrated good acceptance of the grafts with few and moderate extradural fibrosis, which caused adherence of the implants to the bone fragment. No adherence to the cortex was observed. Microscopic examination demonstrated absence of graft adherence to the cortical surface even when the cortex was injured. The cellulose was enveloped by two layers of connective tissue, the external layer being thicker than the internal one. Cellulose fibers increased in thickness over time until 30 days and then decreased in thickness until 270 days. This decrease in thickness between 30 to 270 days was statistically significant (p < 0.05). The physical properties of biosynthetic cellulose and the low cellular reaction to its implantation qualify this material as a dural substitute. Additional long-term studies must be undertaken to complete this report.