New information on the vocalizations and behavior of populations of the Pale-tipped Tyrannulet (Inezia subflava), along with analysis of biometric and plumage characters, reveal that it actually consists of two species-level groups: a northern/Guianan group, the member taxa of which are weakly differentiated from one another; and a group whose distribution is primarily Amazonian, the member taxa of which are morphologically distinct but vocally and behaviorally similar to one another. The two groups differ from one another in several vocal, plumage, and biometric characters. Tape playback experiments suggest that the vocal differences alone present effective mechanisms for reproductive isolation between the two groups. Analysis of vocalizations further suggests a possible link between the Amazonian representatives of Inezia subflava and the Yellow Tyrannulet (Capsiempis flaveola). Received 10 May 1999, accepted 9 Sept. 1999.