A rat model was developed to test the watertightness of sutures. In this model it was proved that welding by use of low-voltage coagulation current did not improve on the watertightness obtained with conventional skin suturing. The mean leak pressure after welding was about 4.2 cm H2O, i.e. statistically significantly lower than the mean leak pressure of the conventional suture, which is 14.1 cm H2O. Neither addition of protein solder nor an additional conventional suture improved these results. It is therefore concluded that low-voltage coagulation is unsuitable for welding tissues.