An absorbable bovine fibrin annuloplasty ring was implanted in the tricuspid position in 30 adult mongrel dogs to determine the rate of absorption and the effectiveness of this new method of annuloplasty. There were 4 early deaths. The remaining 26 dogs survived the operation and were electively sacrificed. The cumulative follow-up was 111.5 months (14 days to one year). Mean follow-up was 4.2 months per animal. Six dogs sacrificed between 2 and 4 weeks (group I) showed mild to moderate ring surface erosion and a fibrinous capsule covering the prosthesis. Nine out of 10 specimens showed total absence of the ring 1 to 2 months after surgery (group II), and all bovine fibrin tissue had disappeared in the 10 remaining dogs after 2 months of implantation (group III). In 2 cases small areas of chondroid degeneration were detected 4 months after surgery. This concept of a time-controlled biodegradable annuloplasty might be useful, although further studies are needed before its clinical application.