We use experimental methods to study the power of leading by words. The context is a voluntary contribution mechanism with one-way communication. One group member can send a free-form text message to his fellow players. Contrary to the commonly accepted wisdom that the cooperation-enhancing effect of communication requires the mutual exchange of promises, we find that the introduction of one-way communication increases contributions substantially and decreases their variation. When communication is one-shot, its effect on contribution levels persists over time. Moreover, one-way communication is effective even in the absence of strategic concerns.