Abstract The IR and 1 H measurements of pyridine perchlorate in acetonitrile as a function of concentration of added pyridine were determined and K app = (K 1 + K 2 K d )/(1 + K d ) = 3.1 ± 0.1 obtained. Equilibrium constant of B + H⋯ A − ⇌B + H + A − was determined by conductometric technique (K d = 1.75×10 −2 moldm −3 ). Using published value of K 2 [B + H + B⇌(BHB) + ] equilibrium constant of B + H⋯A − + B⇌(BHB) + A − reaction, K 1 = 3.1 dm 3 mol −1 , is derived. The discrepancies between published homoconjugation constants of pyridine perchlorate with pyridine are discussed.