The crystal structures of a pair of diastereomeric salts of (2R, 3R)-(+)-tartaric acid and (-)- and (+)-3-N,N-dimethylamino-1,1-diphenyl-1-butanol have been determined. Crystal data: 1: (R)-(-)-C₁₈H₂₄NO⁺, (2R, 3R)-(+)-C₄H₅O^-₆, C2, a = 38.198(7), b = 5.841(2), c = 9.993(2)Å, P = 102.63(1)°, V = 2175.6(1) ų, Z = 4, D_calc = 1.281 g cm^-3. 2: (S)-(+)-C₁₈H₂₄NO⁺, (2R, 3R)-(+)-C₄H₅O^-₆, P2₁2₁2₁, a = 6.037(2), b = 8.5947(8), c = 39.74(1)Å, V = 2062.0(9) ų, Z = 4, D_calc = 1.351 g cm^-3. The conformations of the 3-(N,N-dimethylammonium)-1,1-diphenyl-1-butanol cations in the two salts are almost mirror images of each other, but the cation in 2 has an intramolecular hydrogen bond. The hydrogen tartrate ions adopt an extended conformation. The hydrogen bonding networks in the two salts are very different. The absolute configuration of (-)-3-(N,N-dimethylamino)-1,1-diphenyl-1-butanol (1) was established as R.