The invention relates to pharmaceutical compositions useful in the treatment of benign, premalignant and malignant solid tumours, especially those of the skin, and in the treatment of other disorders of the skin e.g. psoriasis and acne. The compositions comprise at least one catecholic butane. The preferred catecholic butane is nordihydroguaiaretic acid. The compositions are preferably applied topically or by intratumor or subcutaneous injection. The invention also includes sunscreening agents comprising at least one catecholic butane.