The performance of a new compliant microfibrous polyetherurethane urea (Biomer) synthetic artery of our design has been studied in a series of 26 consecutive implants as carotid artery replacements in dogs. A 4 cm length of carotid artery was excised and replaced by a similar length of the synthetic artery. All implants were performed by the same surgeon (LdeC). Twelve interrupted sutures of 6/0 "Prolene" were used to fashion both end-to-end anastomoses. Assessments of patency of the grafts was made using fortnightly Toshiba B scan ultrasound with linked Doppler shift waveform analysis. Twenty-six grafts were implanted. Seventeen grafts have remained patent for periods in excess of 24 months. Five failed acutely (within 2 weeks), 4 failed between the 59th and 201st day. Sixteen of those grafts that remained patent for more than 24 months have been removed for histopathological examination, which has demonstrated a limited extension of a new intima on to the inner surface of the grafts. The new intima is firmly attached and shows no sign of pseudo-intimal hyperplasia. The inner surface, uncovered by neointima, nevertheless, has extensive endothelial cover. Of practical importance are the excellent handling qualities of the graft. It cuts cleanly without fraying and a stitch placed 1 mm from the cut end of the graft will hold securely. There is no needle hole bleeding. The graft has both axial and circumferential compliance similar to that of the natural artery it replaces.(ABSTRACT TRUNCATED AT 250 WORDS)