Kinetics of nucleophilic addition reaction of 9-isothiocyanatoacridine with seventeen aliphatic and aromatic amines in organic solvents has been studied by the VIS spectroscopic method. 9-Isothiocyanatoacridine reacted by about two orders of magnitude faster than phenyl isothiocyanate. The reaction rates of aliphatic amines were markedly affected by steric effects. Excepting 1-acridin-9-yl-3-butylthiourea (