Compounds having a mimetic or antagonistic property of an inositol phosphoglycan, and the uses of these compounds are disclosed, together with the use, e.g. to treat a condition ameliorated by administration of an IPG second messenger or an IPG antagonist thereof. Preferred compounds of the invention are based on the substituted cyclitols, such as the chiro-inositol derivative pinitol (3-O-methyl-chiro-inositol).