This paper attempts to further a better understanding of the piezoresistance coefficients by studying the piezoresistive effects in copper and copper-nickel alloys. The experimental evidence of isotropic piezoresistance coefficients (pi(11) = pi(12)) has been obtained for the annealed copper and copper-nickel alloys. The piezoresistance coefficients of the cold-worked copper and Cu60Ni40 alloy are of the tensor character (pi(11) not equal pi(12)). A physical explanation has been given to the change of the (pi(ij)) tensor.