Metal borides are often decomposition products from metal borohydrides and thus play a role in the reverse reaction where hydrogen is absorbed. In this work, aluminium boride, AlB₂, has been investigated as a boron source for the formation of borohydrides under hydrogen pressures of p(H₂) = 100 or 600 bar at elevated temperatures (350 or 400 °C). The systems AlB₂–MH_x (M = Li, Na, Mg, Ca) have been investigated, producing LiBH₄, NaBH₄ and Ca(BH₄)₂, whereas the formation of Mg(BH₄)₂ was not observed at T = 400 °C and p(H₂) = 600 bar. The formation of the metal borohydrides is confirmed by powder X-ray diffraction and infrared spectroscopy and the fraction of boron in AlB₂ and M(BH₄)_x is determined quantitatively by ¹¹B MAS NMR. Hydrogenation for 12 h at T = 350–400 °C and p(H₂) = 600 bar leads to the formation of substantial amounts of LiBH₄ (38.6 mol%), NaBH₄ (83.0 mol%) and Ca(BH₄)₂ (43.6 mol%).