Attraction and substitution effects have been shown to be important determinants of brand choice when a new brand is added to a choice set. A simple framework is proposed for predicting the effect on relative market shares when a new brand is added to the choice set in an experimental setting. The study attempts to replicate previous results concerning the relative impact of attraction and similarity and to extend empirical findings to brand attribute positionings not examined in recent research on the attraction effect. Generally, the proposed framework operates as hypothesized, and results suggest that, in some instances, a new brand may benefit substantially from the joint effects of attraction and similarity.