Magnetic susceptibility <$E chi> of uranium compounds <$E roman U X sub 3~(X~=~roman {Al,~Ga,~Si,~Ge})> is studied under pressure up to 2 kbar in the temperature range 78 - 300 K. A pronounced pressure effect has been revealed, and the measured volume derivatives, <$E roman {d ln chi "/" d ln V}>, were found to be almost temperature-independent and equal to 2,3, 6,8, and 6,9 for <$E roman {USi sub 3 ,~UGa sub 3 }>, and <$E roman UGe sub 3>, respectively, at 78 K. In <$E roman UAl sub 3>, a noticeable temperature dependence of this derivative was obtained, ranging from <$E roman {d ln chi "/" d ln V}~=~11> at low temperatures to about 5,5 at Т = 300 К. The volume dependent electronic structures of the <$E roman U X sub 3> compounds have been calculated ab initio in the paramagnetic phase by employing a relativistic full-potential LMTO method. The calculations have brought out a predominance of itinerant uranium 5f states at the Fermi energy. The calculated field-induced magnetic moments in <$E roman U X sub 3> and their volume derivatives are in agreement with the experimental data on <$E chi>. An origin of the observed strong temperature dependence of the magnetovolume effect in <$E roman UAl sub 3> is also discussed.Effect of pressure on electronic structure and magnetic properties of <$E {roman Gd} M sub x > (x = 1, 2, 3, 5) systems is studied experimentally and theoretically. By employing the ab initio electronic structure calculations, the magnetic susceptibilities, saturation moments, exchange parameters, magnetic ordering temperature and their pressure derivatives are evaluated and appeared to be consistent with available experimental data. The obtained results are expected to promote further advance in the theory of magnetic ordering in rare-earth systems.Magnetic susceptibility <$E chi> of the isostructural Ce(Ni1-xCux)5 alloys (<$E 0~symbol Г~x~symbol Г~0,9>) was studied as a function of the hydrostatic pressure up to 2 kbar at fixed temperatures 77,3 and 300 K. A pronounced pressure effect on susceptibility is found to be negative in sign and nonmonotonously dependent on the Cu content, showing a sharp maximum at <$E x~symbol @~0,4>. The experimental results are discussed in terms of the valence instability of Ce ion in the studied alloys. For the reference CeNi5 compound the main contributions to <$E chi> and their volume dependence are calculated ab initio within the local spin density approximation, and appeared to be in close agreement with experimental data.