The microeconomic theory relating to utility and cost is applied to the "risk," and the possible "payoff" relative to relationships with others. A good measure of utility is the need or want-satisfying power of an alternative. For the analysis of interpersonal relationships, the needs delineated by Maslow (i.e. food, shelter, belongingness, love, self-esteem, and self-actualization) provide the necessary data to make the interpersonal choice model operational. Thus individuals invest their time and "effort" (emotions) in other people in order to meet their own needs. The Capital Asset Pricing Model (CAPM) is applied to making better interpersonal choices based on the basic investment rule of maximizing the return associated with a given level of risk or minimizing the risk associated with a given return. The only difference in the economic portfolio theory relating to diversification and investment potential is that the investments are made in people instead of stocks. Specific examples of interpersonal choices conclude the article. (Author)