The early stages of the polymerization of 2-[(methacryloyloxy)ethyl]trimethyl ammonium chloride (MADQUAT) in aqueous solution were studied by pulse radiolysis. The rate constant of the reaction of this monomer with OHrad and hydrated electron was measured as 1.5×1010 and 2.2×1010 dm3mol-1s-1, respectively. The absorption spectrum of the OHrad adduct to MADQUAT molecule appeared to have a maximum at 290 nm. Its decay depends on the monomer concentration. The shape and maximum of the absorption spectrum of electron adduct to the monomer depend on pH of the solution. In acidic solution, radical anion is formed. It subsequently undergoes reversible protonation giving spectrum with a maximum below 260 nm. In basic solution the spectrum has a maximum at 290 nm. In this case irreversible protonation takes place at the β-carbon atom, giving an α-centred carbon radical.