Tubulin is an intracellular protein whose in vivo polymerization leads to the formation of microtubules (MT). MT are an essential component of axons of nerve cells. This reaction is the limiting factor in the growth of axons. Uremic neuropathy is characterized in part by an axonal degeneration. A chromatographic fraction from uremic plasma (2–5 fraction) inhibits in vitro the tubulin polymerization and thus MT formation and therefore may be implicated in the occurrence of uremic neuropathy. In vitro, biotin counteracts the inhibitory effect of 2–5 fraction on MT formation. This effect could be a partial explanation of the possible clinical improvement brought on by biotin in uremic neuropathy.