This review provides an up to date information about the diverse pharmaceutical activities of formazans. The bibliography includes 97 references which have been published during the period from 1980 to 2013. The covered biological activities of the title compounds include antioxidant, anticonvulsant, therapeutic, anthelmintic, anti-tubercular, antiviral, anti-inflammatory, anticancer, anti-HIV, antimicrobial, antiparkinsonian, cardiovascular and antiproliferative activities.
Keywords: Biological activity; Formazans; Heterocycles; Tetrazolium salts; azo-hydrazones.