Hexadecyl phosphorylcholine (HPC) micelles incorporate anions rather than cations in the interfacial region, giving an anionoid micelle with a negative zeta potential. Hydronium ion incorporation in the micellar pseudophase parallels the increase in the negative zeta potential, and salts increase the rate of Al hydrolysis of 2-(p-heptyloxyphenyl)-1,3-dioxolane in micellized HPC and inhibit the reaction of OH- with naphthoic anhydride. The kinetic effects are larger with NaClO4 than with NaCl. The increased micellar negative charge with added salts increases the repulsion between headgroups and decreases the aggregation number. These observations are relevant to understanding the behaviors of biological phosphorylcholine amphiphiles.