This paper has aimed to identify marketing variables which affect physicians' prescription of drug. Based on a literature review this paper derives the three factors (indirect commercial source, direct commercial source, academic information source) of information sources that physicians rely on for medicines, the three factors (research supporting activity, marketing supporting activity, medicine information supporting activity) of promotion activities physicians prefer, and the four factors (indirect quality of medicine, direct quality of medicine, experience of using medicine, price and design of medicine) of prescription criteria physicians use. Then it investigates using canonical correlation analysis whether or not physicians' prescriptions are affected by the information sources, the promotion activities, and the type of physicians. From the canonical correlation analysis this paper derives the meaningful three canonical functions of prescription for drugs. The first function explains the prescription which is insensitive to marketing activities, the second function does the prescription which is sensitive to them, and the final function does the prescription which is not affected by them.