A two-chambered cell has been designed and constructed for the measurement of photoresponses of bacteriorhodopsin immobilized in polyacrylamide gel (FAG) membranes. The photoresponse of bacteriorhodopsin was determined by measuring the pH variation in each chamber independently, for long periods of illumination. The aim was to verify the light driven proton transfer of bacteriorhodopsin immobilized in FAG membranes. However, the same pH variation was observed in the two chambers irrespective of whether oriented or nonoriented bacteriorhodopsin immobilized in FAG membranes were employed. It has been concluded that upon illumination of the biosynthetic membrane, protons were not transfered from one chamber into another. The pH variation was then attributed to the association and dissociation of protons from bacteriorhodopsin in the membrane. The protonation and deprotonation of FAG interfered with the photoresponse of bacteriorhodopsin due to pH disturbance, even though light had no direct effect on FAG. This might be the main reason for the very low efficiencies obtained in such energy transducing biosynthetic membranes.