Isonicotinic acid or 4-pyridinecarboxylic acid is an organic compound with the formula C5H4N(CO2H). It is a derivative of pyridine with a carboxylic acid substituent at the 4-position. It is an isomer of picolinic acid and nicotinic acid which have the carboxyl group at the 2- and 3-position respectively compared to the 4-position for nicotinic acid.
