drug diffusion mechanism through phsensitive hydrophobicpolyelectrolyte hydrogel membranes methylmethacrylatedimethylaminoethyl methacrylate crosslinked with divinylbenzene is a phsensitive hydrogel we have studied the diffusion mechanisms of drugs with different water solubilities through this hydrogel a watersoluble model drug aminopyrine was used to study the diffusion coefficient changes in different phs the results showed a watercontent dependent diffusion for this phsensitive polycationic hydrogel however decreasing the solubility of the drug and increasing the hydrophobic character of the polymer by changing the ph caused a greater affinity or partition coefficient between the hydrogel and the drug aminopyrine diffusion was shown to follow the freevolume theory suggesting the pore type mechanism for water soluble drugs while the partition or solutiondiffusion mechanism better described the slow diffusion of water insoluble solutes through this phsensitive hydrogel comparing the swelling interface number for aminopyrine release through this phsensitive hydrogel showed a nonfickian mechanism in the hydrated form of the hydrogel ph 12 while fickian in the dehydrated form ph 74