The invention is directed to substantially pure fluorescein, substantially pure fluorescein compositions and to pharmaceutical compositions for use in angiography. A substantially pure fluorescein is provided which is low in colour, low in sodium chloride content, and substantially free of pyridine. Fluorescein comprised in the composition is defmed as substantially pure if there are no detectable fluorescein-related substance impurities, or if a single fluorescein-related substance impurity is detected, it is present in an amount no greater than 0.1 % by weight, or if multiple fluorescein-related substance impurities are detected, they are present in aggregate in an amount no greater than 0.6% by weight, and wherein said fluorescein-related substance impurities comprise synthetic impurities arising from the reaction of resorcinol with succinic acid (as an impurity in the phthalic acid precursor for fluorescein) isomers, oxidation products, dimerization products, and decomposition products of fluorescein.
