This paper deals with the modification of the AM2 model (Bernard and al. (2001)) to integrate the production and the degradation of the Soluble Microbial Products (SMP) in an Anaerobic Membrane BioReactor (AMBR). The developed model takes into account the characteristics of membrane bioreactors, namely i) there is no biomass in the effluent, ii) part of the SMP, corresponding to the biggest molecules, is retained in the reactional medium, iii) the decay rate and the withdraw of the biomass are considered. Possible equilibria of the system are calculated, and the influence of the maximum growth rate of the biomass on the SMP on these equilibria is analyzed. It is shown that the presence of this new variable in the model changes the qualitative properties of the classical AM2 model.