Corneal ulcers me major problems in our country, the patients usually seek medical advice late, so most of these ulcers usually resist medical treatment and therapeutic keratoplasty may be the only procedure to preserve the eye both anatomically and functionally. In this study we examined 30 corneal buttons removed by therapeutic keratoplasty from patients suffering from corneal ulcers resistant to medical therapy Examination was done using light microscopy for sections stained with H and E, PAS and silver stains. Bacterial infection was suspected in 43.3% of the specimens, viral etiology in 33.3%. and Acanthamoeba in [13.4%]. Three buttons [100%] proved to be of fungal aetiology [as demonstrated by PAS stain] This study indicates the importance of Histopathologic examination of corneal buttons inpatients undergoing therapeutic keratoplasty for resistant corneal ulcers and this may help the physician to know the etiology of these ulcers and to select the ideal post operative antimicrobial therapy