A clinical trial of a collagen-sealed knitted Dacron conduit (Tascon Medical Technologies) in 86 patients has revealed a high incidence of early reoperation for conduit stenosis. At 3 years, the actuarial incidence of freedom from conduit replacement was 67 +/- 14% for valved conduits, and 66 +/- 20% for nonvalved conduits. Seven of eight conduits that were replaced had a thick, weakly adherent pseudointima. Comparison of the current series with a previous series of patients receiving tightly woven low-porosity Dacron conduits is complicated by the young age, small size, and greater complexity of the current group. Nevertheless, the findings are consistent with the results of two laboratory studies performed at this hospital which suggest that the collagen used in the Tascon conduit undergoes particularly slow resorption, resulting in weak adhesion between the pseudointima and conduit. This allows hemorrhagic dissection to occur deep to the pseudointima. These data suggest that alternative methods of sealing knitted Dacron conduits should be used.