The research reported here examined the effects of two potential motivators of political activism—policy change threat and policy change opportunity—in a field experiment. Different versions of a letter were sent by a political lobbying organization to potential contributors. One version highlighted threats of undesirable policy changes, another version highlighted opportunities for desirable policy changes, and the third version did neither. Policy change threat increased the number of financial contributions made to the interest group, but policy change opportunity did not. Policy change opportunity increased the number of signed postcards returned to be sent to President Clinton, but policy change threat did not. These findings highlight the impact of interest group recruitment strategies on citizen responsiveness and demonstrate the need to account for sources of motivation in order to more fully understand when, why, and how citizens choose to become politically active.