In order to evaluate the function of the retina in Best macular dystrophy (BMD) 18 patients were examined by means of the multifocal electroretinogram (mfERG). The mfERG peak amplitudes of the central and pericentral responses were significantly reduced in the BMD patients (p<0.001). The ERG amplitude decrease of the central response was significantly correlated with visual acuity loss and with the funduscopic staging. The implicit times in more eccentric groups were slightly but significantly increased. The markedly reduced mfERG amplitudes with only slightly increased implicit times may indicate cone photoreceptor cell loss or damage to the cone outer segments.