Pharmacology is characterized by understanding biological phenomena based on interactions between compounds (including drugs) and biological macromolecules (mainly proteins). This is a unique perspective of pharmacology distinct from other life sciences. Drug discovery research is carried out as a practice of this pharmacological viewpoint. Drug discovery targets are identified based on pathological analysis in drug discovery research. Clinicopathological relevance studies of the presumptive therapeutic target play an important role in target evaluation. The pharmacologists evaluate the target molecule concerning the histopathological image, clinical symptoms, and clinical course and prognosis. This is crucial in target validation, together with gene manipulation studies and model drug treatment experiments in experimental animal disease models. In preclinical studies, pathological analysis is also essential for pharmacological efficacy evaluation of development compound candidates. In drug discovery research, it is essential to evaluate the interactions between drugs and drug targets in pathological conditions. Detailed pathological analyses concerning drug effects could be expected to reveal new aspects of drug action. Moreover, such analyses would facilitate the development of more optimized drugs.