INDAZOLES (BENZOPYRAZOLES), in chemistry, are crystalline, feebly basic organic compounds. Indazole itself has formula (I.) and is prepared by warming an aqueous solu tion of o-toluenediazonium chloride (see DIAZO CoMPouNps). It is a crystalline solid melting at 146° C (boiling point, 27o° C). This ring formation is exhibited only by diazonium salts having a methyl group adjacent to the diazo-radical. A series of isomeric compounds, isoindazoles, is known ; the acetyl derivative of the simplest member (formula II.) is made by warming o-amino benzaldoxime with acetic anhydride (see PYRAZOLES).