If isospin invariance is not assumed in neutron-proton scattering, then a termf(E,θ)(σ1—σ1n will be present in the scattering amplitude. Experiments detecting the amplitudef(F, θ) are discussed, the simplest of which from the present-day experimental point of view are different proton and neutron asymmetries in the scattering of polarized neutrons on polarized proton targets. The contributionsfem(E, θ), due to one-photon exchange (with all proton and neutron form factors), andfope(E, θ), due to electromagnetic nucleon and meson mass differences in the one-pion exchange, are calculated. The calculated amplitudefem+fope is used together with neutron-proton amplitudes obtained from phase shift analyses to predict the behaviour of “the isospin violating” experimental quantities.