Abstract: The invention relates to methods useful in the treatment of benign, premalignant and malignant solid tumors, especially those of the skin comprising methods for the administration of pharmacologically active compositions containing catecholic butanes. The invention also relates to methods of preventing the occurrence of tumors, and the use of catecholic butanes as a sunscreening agent. The preferred catecholic butane is nordihydroguaiaretic acid. The preferred methods of application of the compositions containing catecholic butanes are by topical application and intratumor injection.