The parent stars of the recently announced planetary system candidates are far from typical in terms of their chemical compositions. In this study we report on spectroscopic abundance analyses of upsilon And and tau Boo. Both stars are metal-rich relative to the Sun, with a mean [Fe/H] value near 0.25. These findings follow the trend set by two other planetary system candidates, rho^1 55Cnc and 51Peg, which also display metallicities much higher than the average for nearby dwarfs. In addition, their companions share similar orbital characteristics. Given these observations, we propose that the current metallicities of these four stars are not representative of that of the original interstellar clouds from which they formed but, rather, are the result of self-pollution during the planet formation epoch early in their histories.