The critical current densityJcof 0.25‐mm Cu88.5Nb10.0Sn1.5and Cu83.5Nb15.0Sn1.5wires has been measured at 4.2 °K as a function of magnetic fieldHup to 100 kG. A typical value ofJcatH= 0 is ∼105A/cm2indicating that the critical current density of the Nb3Sn filaments is probably of the order of 106A/cm2. Mechanical deformation such as bending some of the wire samples around a 1/2‐in.‐diam mandrel does not produce any significant degradation ofJcatH=40 kOe.