"Normal healthy research volunteers" (NHRVs) in Phase I clinical trials are utilized to provide precise pharmacokinetic information and subjective self-reports to help determine the initial drug dose for future Phase II, III, and IV trials, and accurate dose levels for future use in a patient population. Medical researchers rely on both objective pharmacokinetic and subjective data from NHRVs. Research shows that personality characteristics can influence these results in Phase I clinical trials. For example, extroverted personality characteristics have influenced the subjective reports and physiological experience of NHRVs. Second, subjective responses to placebos have been significantly greater in extroverted NHRVs than in introverted NHRVs. Third, in looking at Type-A and Type-B personality characteristics, NHRVs with Type-A Characteristics reported significantly more negative side effects to placebos than did people with Type-B characteristics. Fourth, NHRVs with high anxiety had more reports of adverse symptoms after drug administration than NHRVs with low anxiety. Further, it has been found that gastric emptying occurs more rapidly in people with high levels of neuroticism as compared to people with low levels of neuroticism. The authors suggest that personality and psychological characteristics of NHRVs can influence pharmacokinetic results and thus need to be addressed either in the statistical analysis or in the screening process for NHRV studies. Suggestions for further research and analysis are included, along with ideas for a national volunteer subject pool for NHRVs.