This report describes a series of 101 femoropopliteal bypasses performed on 85 patients (16 bilateral procedures), in whom a 6 mm diameter polytetrafluoroethylene prosthesis (Goretex) was used. The indication for operation was severe claudication in 58 cases and pregangrene in 43 cases. After one year there was a statistically significant difference between the cumulative patency rates for these two subgroups at 66 and 29 per cent respectively (P less than 0.001). In patients with good 'run-off, i.e. three patent vessels in the lower leg, there was a tendency for the bypasses to remain patent for longer than in patients in whom there were only one or two vessels present (e.g. 58 and 33 per cent respectively at 2 years), although this trend was not statistically significant. At 3 years the cumulative patency rate for the whole group was 36 per cent and for claudicants alone was 48 per cent.