Mittal R, et al. – The goals of this study are to explain the histopathology of Pythium insidiosum keratitis and to depict a novel, simple, and rapid staining technique for identification of oomycete Pythium insidiosum and to differentiate it from fungi. Pythium insidiosum keratitis is perhaps not more devastating than fungal keratitis but late diagnosis, misdiagnosis, and treatment of fungal infection are major heralds. The patient outcome may markedly improve by early diagnosis. IKI–H2SO4 is a cost–effective, simple, sensitive, and specific stain for the diagnosis of oomycete Pythium.