A combined resistivitytransmission electron microscopy(TEM) study has been done on heavily drawn Cu‐20 vol % Nb alloys (so‐called i n s i t u alloys). The results show that electron scattering at Cu‐Nb interfaces makes the major contribution to resistivity in heavily drawn wire. The dislocation contribution is small and constant at deformation strains greater than around 4, apparently as a result of dynamic recovery/recrystallization of the Cu matrix which occurs during room‐temperature drawing. Results of this study and other recent TEM dislocation studies indicate that the dislocation density in heavily drawn Cu‐20 vol % Nb material does not exceed 10^{1 1} cm^{− 2}. It is demonstrated here that the 10^{1 3}‐ cm^{− 2} dislocation density predicted by the resistivity study of Karasek and Bevk [J. Appl. Phys. 5 2, 1370 (1981)] is high because the interface scattering contribution is more strongly reduced by coarsening than they assumed. It is shown that resistivitymeasurements provide a means of evaluating an average Cu channel diameter in the aligned composite alloys formed at large deformation strains.