Between-partner physiological linkage can be in-phase (changes in unison), or anti-phase (changes in opposite directions). In the context of conversation we predicted that in-phase linkage would occur when partners exert strong influence on each other; anti-phase linkage would occur due to the behavioral coordination of turn taking. To test this, blood pressure, inter-beat interval, and skin conductance were recorded from 44 heterosexual couples while they discussed how they influence each other's health-related behaviors. Partner influence was assessed in two ways: 1) partners' global perceptions of how they try to influence each other's health; and 2) behavioral manifestations of influence, specifically demand-withdraw behavior. As predicted, both measures of partner influence moderated physiological linkage of blood pressure such that at low levels of influence linkage was "anti-phase" and at high levels linkage was "in-phase." Several alternative hypotheses were ruled out; the effects were not due to relationship conflict, emotional experience, or simply the pattern of blood pressure over time. These results suggest that partner influence may be driving physiological linkage, which may be one avenue through which partners can affect each other's health.