Dialkylaminium cation radical kinetics were studied directly by laser flash photolysis methods. Irradiation of N-hydroxypyridine-2-thione carbamates with 355-nm light gave dialkylaminyl radicals that were protonated to produce dialkylaminium cation radicals. Fragmentation of the N-ethyl-2,2-diphenylethylaminium cation radical (2A) and cyclizations of the N-methyl-5,5-diphenyl-4-pentenaminium cation radical (6A) and the N-methyl-6,6-diphenyl-5-hexenaminium cation radical (9A) were studied. In organic solvents, these reactions are several orders of magnitude faster than analogous reactions of their neutral dialkylaminyl radical precursors and faster than reactions of isostructural carbon radical analogs. In acetonitrile and in THF with carboxylic acids as proton sources, reactions of 2A and 9A displayed saturation kinetics from which rate constants for reaction and apparent equilibrium constants for protonation could be determined by regression analysis of observed rate constants as a function of acid normality. In ethanol with perchloric acid, 9A was completely protonated. In aqueous solutions, the observed kinetics for reactions of 2A and 9A were dependent on the pH of the solutions which permitted determinations of both the rate constants for the reactions and the pK(a) values for the dialkylaminium cation radicals.