A chitosan for use in an antimicrobial treatment of a patient's tissue and a pharmaceutical composition comprising a chitosan for use in an antimicrobial treatment of a patient's tissue. A method of treating a microbial infection, the method comprising the step of administering to a patient an effective amount of a chitosan and an aqueous solution comprising chitosan. A chitosan or a pharmaceutical composition comprising a chitosan for use in an epithelial cell growth stimulating treatment of a patient's tissue. A method of stimulating the growth of epithelial cells the method comprising the step of administering to a patient or to an epithelial cells containing cell culture an effective amount of a chitosan or a pharmaceutical composition comprising chitosan. A tissue dressing material characterized in that it consists of chitosan or a chitosan comprising composition.