: IdoA) is the major uronic acid component of the glycosaminoglycans (GAGs) dermatan sulfate, and heparin.

It is also present in heparan sulfate, although here in a minor amount relative to its carbon-5 epimer glucuronic acid.

[citation needed] IdoA may be modified by the addition of an O-sulfate group at carbon position 2 to form 2-O-sulfo-l-iduronic acid (IdoA2S).

In 2000, LK Hallak described the importance of this sugar in respiratory syncytial virus (RSV) infection.

Proton NMR spectroscopy can be used to track changes in the balance of this equilibrium.