The permeability characteristics of the strongly basic polymer membrane Neosepta(R) AFN-7, (Tokuyama Soda) have been studied for acetic, propionic, lactic, tartaric, oxalic, and citric acid. The results were interpreted by using the model of transport in reactive membranes. The specific constants, that is, the maximum flux J(max) the reactivity constant K, and the permeability coefficient (P), were calculated using the experimental quasi-stationary fluxes and the equation derived as a sum of reaction-diffusion (Michaelis-Menten-type), and the solution-diffusion transport equation. The constants K and J(max) were found to range from 0.1 to 5 dm(3) mol(-1) and from 0.4 x 10(-7) to 2.5 x 10(-7) mol cm(-2) s(-1) depending, on the acid properties. The values of K and J(max) were correlated with the dissociation constants K-dis.acid, and the diffusion coefficients D-aq.acid in aqueous media, respectively. It was found that the reaction-diffusion flux is predominating for all acids, except for the lactic one, when the feed concentration is lower than 0.5 mol dm(-3).