The present study investigates the possible existence of a systematic relation between beta and excess-return for portfolios of Turkish equities. In the process, no systematic relation is found between beta and realized portfolio excessreturn, in an unconditional sense. However, the study does find a systematic relation between realized portfolio excess-return and beta, conditioned upon the sign of realized market-portfolio excess-return. Moreover, an even stronger systematic relation is found between realized portfolio excess-return and beta, conditioned not only upon the sign, but also the magnitude of realized market-portfolio excessreturn, with the estimation of the security market plane (SMP) model. The study has several useful implications for portfolio managers. Firstly, the empirical findings strongly suggest that employment of the SMP model may generate more accurate estimations of expected asset-return, compared with straightforward application of the capital asset pricing model (CAPM). Enhanced accuracy of expected asset-return, in turn, may lead to more accurate appraisals of asset value, resulting in more profitable investment opportunities and decisions. Employment of the SMP model may thus lead to enhanced efficient-portfolio development, by leading to construction of portfolios with greater expected-return, for a given class of quantifiable-risk.