The purpose of this study was to examine whether initially low levels of support behaviors observed among cohabitating and married African American couples significantly predicted higher levels of negative behaviors (specifically hostility) in their interactions two years later. In addition, the analyses examined whether these later levels of hostility predicted relationship satisfaction over time. That is, did supportive behaviors serve a protective function in terms of their impact on the longitudinal course of marriage and cohabitation? The results of the structural equation modeling analyses provided some support for these hypotheses, as the level of initial support behaviors displayed by the female partner was a marginally significant predictor of her level of hostility at Wave 2 but not his later level of hostility; as her level of initial support increased, her level of hostility at a later time point decreased. In addition, level of hostility displayed by the male partner at Wave 2 was a marginally significant predictor of his relationship satisfaction, with higher levels of hostility at Wave 2 significantly predicting lower relationship satisfaction at Wave 2. The results of the current study indicate significant contributions of support to relationship functioning and demonstrate potential gender differences in the role of support on later communication behaviors and relationship satisfaction.