Two studies tested whether action control by implementation intentions is sensitive to the activation and strength of participants' underlying goal intentions. In Study 1, participants formed implementation intentions (or did not) and their goal intentions were measured. Findings revealed a significant interaction between implementation intentions and the strength of respective goal intentions. Implementation intentions benefited the rate of goal attainment when participants had strong goal intentions but not when goal intentions were weak. Study 2 activated either a task-relevant or a neutral goal outside of participants' conscious awareness and found that implementation intentions affected performance only when the relevant goal had been activated. These findings indicate that the rate of goal attainment engendered by implementation intentions takes account of the state (strength, activation) of people's superordinate goal intentions.