The reaction of butylmercury nitrate with organic bases has been studied in four solvents. BuHgNO3 is molecular in benzene and acetone but ionic in water; in acetonitrile there is an equilibrium between molecular and ionic species. In benzene solution bases form 1 : 1 adducts, 3-coordinate with pyridine, 4-methylpyridine, bipyridine, Et3N, Bu3N, PBu3, PPh3 or diphos, 4-coordinate with tetramethyldiaminoethane. Adduct stabilities and enthalpies of formation are reported. In acetone solution bases displace nitrate, in water bases displace coordinated water and in acetonitrile they displace nitrate or coordinated solvent; in all three solvents the end products are BuHg · base+ and NO3-. Enthalpies are reported for these reactions. Distribution of BuHgNO3 between benzene and water is concentration dependent. Addition of phosphines increases the proportion of the mercury in the benzene phase; addition of heterocyclic bases increases the proportion in the aqueous phase; addition of tertiary amines first increases the proportion in the benzene phase, then, with higher base concentrations, that in the aqueous phase. © 1978.