Progress in the identification and characterization of new carboxy-terminal motor domain type kinesin superfamily proteins (KIFs)-KIFC2, 16 new KIFs and KIF-associated protein 3 (KAP3)-has provided further insight into the molecular mechanisms of organelle transport in neurons. Developments in molecular and cellular biophysics and recombinant adenovirus infection techniques combined with transgenic mice technology have enhanced the visualization of moving forms of cytoskeletal proteins during slow transport. The results of these studies strongly support the subunit transport theory.