The electron screening in the d(d,p)t reaction has been studied for the deuterated metal Pt at a target temperature T = 20 degrees C to 340 degrees C, and for Co at T = 20 degrees C and 200 degrees C. The enhanced electron screening decreases with increasing temperature, where the data agree with the plasma model of Debye applied to the quasi-free metallic electrons. The data represent the first observation of a temperature dependence of a nuclear cross-section. We also measured the screening effect for the deuterated metal Ti (an element of group 4 of the periodic table) at T = -10 degrees C to 200 degrees C: above 50 degrees C the hydrogen solubility dropped to values far below unity and a large screening effect became observable. Similarly, all metals of groups 3 and 4 and the lanthanides showed a solubility of a few percent at T = 200 degrees C (compared to T = 20 degrees C) and a large screening became also observable. Within the Debye model the deduced number of valence electrons per metallic atom agrees with the corresponding number from the Hall coefficient, for all metals investigated.