Cajal and contemporary scientists have laid the basis of the modem concepts of the organization of the nervous system: the cir­ cuits of the brain are made up of individual neurons which transfer information via specialized structures called synapses. Soma and den­ drites usually receive the inputs, then the signal is carried all along the axon to the target areas. To fulfIll this task several types of neurons have developed their unique geometry characterized by a large recep­ tive area (soma and dendrites) and an often very extensive distal branching with the axon terminals. The volume of cytoplasm which constitutes the neuronal periphery is often far larger than the cell body, where the synthetic machinery is located. It is one of the roles ofaxoplasmic transport to supply the periphery with proper material and to sustain the specialized structures necessary for the physiological activity of the neuron. Furthermore, it has become more and more clear that target areas also exert effects on the innervating neurons, and these effects are not only mediated via recurrent fibers. Synapses have been shown to be able to pick up material from the synaptic left which is then intra­ axon ally transported back to the cell body. This retrograde axoplasmic transport has therefore been recognized as another basic mechanism to convey signals from the periphery to the centre.