Chemically, auxin a is auxentriolic acid (C18H32O5) while auxin b is auxeniolonic acid (C18H30O4). In plants however auxin a and b are hardly known. Heteroauxin which is chemically IAA (C10H902N), is the principal naturally occurring hormone in higher plants.

In addition to IAA, several other related compounds and derivatives have also been reported from plants. These are Indolebutric acid (IBA), Indole 3 acetaldehyde, Indoel – 3 ethanol, 4 Chloro IAA etc.