Abstract: This invention relates to salts of guanidine derivatives of formula R—X—C(?NH)NH3+Z?, wherein X represents a valence bond, —CH2—NH—, —CH2—NH—NH— or —CH?N—NH—; R represents a linear or branched C1–C30 alkyl, C3–C20 cycloalkyl, adamantyl, norbornyl, tricyclodecyl, benzyl, furyl, pyridyl, anthracyl, naphthyl, phenanthryl, perinaphthyl or quinuclidinyl residue, which can be substituted by one or more hydroxyl groups, C1–C4 alkoxy groups, C1–C4 alkyl groups and/or one or more halogen atoms or one or more amino groups; Z represents O—CO—Y, O—S(O)2—Y, or O—P(O)(OH)—Y; and Y represents a linear or branched C1–C12 alkyl, C3–C8 cycloalkyl, benzyl, furyl or pyridyl residue, which can be substituted by one or more hydroxyl groups, carboxylic acid groups, C1–C4 alkoxy groups, C1–C4 alkyl groups and/or one or more halogen atoms or one or more amino groups. These compounds are useful for treating tumor diseases, autoimmune diseases, cardiovascular diseases, infections, and viral diseases.