The purpose of this study is to clarify the benefit and loss for the pharmaceutical companies when they adopt introducing pharmacogenomics in their clinical trials (in the following description, clinical trials by using pharmacogenomics is called "pgx clinical trial"), that is, when they use genetic information in their clinical trials. Particularly, the benefit for the pharmaceutical companies in terms of following two points is analyzed. 1. Development cost of new drug and period of clinical trial can be reduced because a clinical trial needs less subjects, 2. The new drug can be placed on the market earlier because the development period can be shortened. A survey conducted by Japan Pharmaceutical Manufacturers Association revealed that the pharmaceutical companies in Japan are interested in "pgx clinical trial". Specifically, 95% of the member companies (n=19) of the Association replied that the establishment of a guideline for pgx clinical trial by regulatory authorities are highly desirable. However, 65% of them (n=13) also replied that pgx clinical trial is difficult for the time being. It can be concluded that the pharmaceutical companies are positive about pgx clinical trial, but they cannot take a step towards it for several reasons: some of them may be worried their sales for non-responders will be reduced, poor understanding of pgx among the concerned parties, and not matured methodology of pgx clinical trial. This study shows that the advantage of pgx clinical trial outweighs its disadvantage. The sales may decrease because the drug is not used for non-responders, however, the number of subjects necessary for a clinical trial can be reduced, study period can be shortened and the drug can be marketed earlier. Furthermore, adverse events (AE) and adverse drug reactions (ADR) during the clinical trial and post-marketing phase can be markedly reduced. This represents a great benefit for the patients, pharmaceutical companies and thesociety as a whole.