Magnetic susceptibility of ferromagnetic GdM alloys (MMg, Zn, Cd, and Cu 1−x Ga x ) has been investigated under pressure for temperatures above T C . The evaluated pressure derivatives of the paramagnetic Curie temperature appeared to be remarkably different for isovalent GdM compounds. Analysis of the experimental data and results of ab initio electronic-structure calculations for GdMg and GdZn have revealed the essential role of 5d electrons as the mediators of exchange coupling in ferromagnetic GdM compounds. The pressure derivatives of T C were calculated by employing a spin fluctuation theory. As a result, a good agreement is found with the experimental data.