Selective degeneration of mitral cells, the principal relay neuron in the central olfactory pathway, is described in the mutant mouse Purkinje cell degeneration (PCD). Concomitant effects are described in adjacent layers of the olfactory bulb which suggest a reorganization of local neuronal circuits. The 2-deoxyglucose technique produced results which suggested that the topographical distribution of sensory afferent input to the bulb was not affected.