A novel carboxybetaine monomer, 4-(2-acrylamido-2-methylpropyldimethylammonio) butane ate (AMPDAB), has been synthesized and copolymerized with acrylamide in an aqueous NaBr solution. The feed ratio of AM (M(1))/AMPDAB(M(2)) was varied from 90/10 to 0/100 mol%. Low conversion samples were collected and copolymer compositions were determined with C-13 n.m.r. by integration of the carbonyl resonances. Reactivity ratios were determined and the nonlinear least-squares method yielded values of r(1) = 1.01 and r(2) = 0.99, indicating random incorporation of monomers into the final copolymer. Molecular weights were determined and range from 3.9 to 12.0 x 10(6) g mol(-1). The solution behaviour of the above copolymers was studied as a function of pH and added electrolytes. With the exception of the copolymers containing 60 and 75 mol% AMPDAB, homogeneous solutions were obtained in deionized water. At high pH, the polyzwitterions show an enhancement in viscosity as the concentration of added electrolyte is increased. In deionized water, as the pH of the aqueous media is lowered, the copolymers exhibit a dramatic increase in viscosity as the carboxylate groups are protonated and charge-charge repulsions of the quaternary ammonium groups induce polyelectrolyte behaviour. The solution behaviour is compared to structurally similar sulfobetaines which do not exhibit any responsiveness to changes in pH.