The phase diagrams of the V-Si and Nb-Si alloys were established by thermal anal., x-ray, and microscopic examn. Alloy specimens were prepd. by sintering under pressure, by converting cold-pressed powder mixts. into solids in an A atm., and by melting the metals in arc furnaces. A eutectic between Si and the compd. VSi2 occurs with 5 wt. % V at a temp. of 1385°. Pure tetragonal V5Si3 was assigned to the space group D2d11 with lattice consts. a = 9.410 and c = 4.747 kX units. The VSi2 and V3Si phases were confirmed. In the Nb-Si system, a eutectic occurs with 8 wt. % Nb which melts at 1405°. Only the compds. Nb5Si3 and NbSi2 were identified; the transition of β- into α-Nb5Si3 at approx. 2000° has led to previous reports of other compds. β-Ni5Si3 belongs to space group D2d11 with a = 9.998 and c = 5.067 kX units. A change in crystal habit accompanies the transformation into platelets of α-Ni5Sb3 which belongs to space group D4h18 with lattice consts. a = 6.557 and c = 11.860 kX units. The tetragonal compds. V5Si3, α-, and β-Nb5Si3 are converted into a ternary hexagonal phase by the addn. of only 0.1-0.2% C, which has a relatively extensive homogeneity range.