Cholinergic neurons, and their relationship to microglial cells, have been examined by light and electron microscopy with an immunocytochemical and histochemical double-staining technique, in medial septum, diagonal band of Broca, nucleus basalis and neostriatum. This technique may be applied to experimental models of anterograde and retrograde degeneration of the cholinergic neurons of the basal forebrain in order to collect further information relative to the aetiology of degenerative diseases such as Alzheimer's disease.