Microtubules are directly involved in many basic processes of eukaryotic cell function including division, growth, and locomotion of cells, and organelle transport. As a consequence, the study of microtubule function has become a major field of cell biology. The squid giant axon has recently been introduced as the ideal system to study microtubules and microtubule-associated motility such as organelle transport. At the same time this preparation made axoplasmic transport one of the most important paradigms for the study of all microtubule-based motility.