This study employs CCA (Contrastive Conversation Analysis), described by Maynard (1990), to study native-English speakers' and native-Spanish speakers' use of back-channel responses, both in mixed-sex and single-sex conversational pairs. The data sample consists of a total of eight tape-recorded conversations among eight participants, consisting of four native-English speakers from the United States and Canada, two of whom are male and two of whom are female, and four native-Spanish speakers from Chile and Argentina, two of whom are male and two of whom are female. The back-channels produced by participants are categorized as being one of two kinds: "In-Between" back-channels, inserted during pauses in the speech of the interlocutor who holds the floor, or "Overlap" back-channels, uttered while the interlocutor who holds the floor is still speaking. Seven of the eight participants produced both more In-Between and more Overlap back-channel responses in mixed-sex conversation than in single-sex conversation. The Spanish-speaking female participants exhibited the greatest increase in back-channel production from single-sex to mixed-sex conversational pairs, followed by the English-speaking females, the English-speaking males, and finally the Spanish-speaking males. Careful examination of the data reveals that a greater increase in back-channel production in mixed-sex conversation corresponds to a greater accommodation to the style of back-channel behavior of the opposite-sex conversational partner. Therefore, the author finds that Spanish-speaking females accommodate their back-channel behavior the most, followed by English-speaking females, English-speaking males, and finally Spanish-speaking males.