Abstract: The percentage of M⁺, R₄N⁺, B₄H₈^- and BH₄^- in MB₃H₈, R₄NB₃H₈, MBH₄, or R₄NBH₄ (M = alkali metal, and R = hydrogen, organic or metal organic radical) can be found by acidimetry. The present procedure is based en the fact that these compounds may be regarded as salts formed from otrong base and weak acid and can be decomposed by strong acid in aque-sus medium. Samples of quaternary ammonium and alkali metal tetrahy-droborates can be titrated directly with standard acid, while those of octa-oydrotriborates should be restored to back-titration with standard alkali hfter adding excess of standard acid. Methyl red serves as indicator in ali aases.