We investigated vocal communication between males in a central Indiana population of the green frog, Rana clamitans. Three playback experiments were conducted. In the first test, we broadcasted a single-note and a multiple-note conspecific acvertisement call and a control call (Acris crepitans) to calling males. In response to the conspecific stimuli, males increased the number of calls made per minute, increased note duration, lowered the dominant frequency in the call, and often approached the speaker platform. In a second playback test, designed to examine changes in the sound pressure levels of response calls, we broadcasted a conspecific single-note advertisement call and the control call to calling males. Males in this test lowered the intensity of their responses to the conspecific stimulus. We take these altered response calls to be encounter calls used in the vocal defense of a territory during agonistic male-male interactions. We examine the function of these calls and discuss their possible role in communication between males, In the third test, we broadcasted a second type of conspecific multiple-note call and the control call. In their responses, males increased the number of the second multiple-note calls. The multiple-note stimulus used in this test failed to elicit the agonistic responses of the first two conspecific calls. The role of his second type of multiple-note call in male-male communication remains unclear.