The so-called T-odd correlations in leptonic decays of hadrons due to electromagnetic final state interaction have been calculated. Analysis of these correlations is of interest since they form a masking background for the effects due to possible CP-violation. An accurate measurement of T-odd correlations in K_μ3 ⁰-decays would in principle allow to determine the electrical radius of the π-meson and in Ξ^- → Λeν-decays the magnetic moment of the ΣΛ-transition. However, to get this information the existing statistics of the decays should be increased by four orders of magnitude in the first case and by eight orders in the second case.