Indolyl-3-acryloylglycine, also known as trans-indolyl-3-acryloylglycine, or IAG for short, is a compound consisting of an indole group attached to an acrylic acid moiety, which is in turn attached to a glycine molecule.

This compound has been shown to isomerize when exposed to light.

[3] It may also be produced by certain elements of the mammalian gut microbiota by phenylalanine ammonia-lyase.

[4] Identifiable in the urine by high-performance liquid chromatography, it may be a biomarker for autism spectrum disorders, as demonstrated by the research of Paul Shattock[5][6][7] and other researchers from Australia.

[8] These researchers have reported that urinary levels of IAG are much higher in autistic children than in controls; however, other researchers have found no association between IAG concentrations in the urine and autism.