An electrochemical quartz crystal microbalance study of platinum phthalocyanine thin films in aqueous media is presented. It has been shown that these films exhibit significant mass changes upon electrochemical cycling. These mass changes have been shown to be controlled by the ingress and egress of solvated anions during oxidation and reduction of the film, respectively. The mass changes within the film are shown to tend to steady state after a prolonged period of cycling. Chrono-amperometric studies have additionally shown that the movement of cations also has a role in the electrochemistry and mass transport within these films, but generally these events occur on a shorter timescale than those involving the solvated anions, and are hidden during most potential cycling studies. (C) 2009 Elsevier B.V. All rights reserved.