SummaryGeographic variation in the Zebra FinchTaenio-pygia guttatawas examined by comparing live wild-caught and captiveT. g. guttatafrom the Lesser Sunda Islands in Indonesia andT. g. castanotisfrom the Australian mainland and confirmed by museum skin measurements ofguttataandcastanotis.(1)T. g. castanotisis significantly larger thanT. g. guttata, as measured by wing length, weight and bill length. (2)castanotishave redder, darker, brighter bills thanT. g. guttata.(3)T. g. castanotismales have larger breast-bands thanT. g. guttatamales, even when the size difference is taken into account, with strongly pronounced black barring on the throat and upper breast which are absent fromT. g. guttatamales on Lombok, Sumbawa, Flores and Timor. (4)T. g. castanotisproduce lower frequency distance calls and the males differ fromT. g. guttatamales in having a noise part to this call. (5) The songs of captiveT. g. castanotismales are lower in frequency and their song phrases are shorter, with fewer elements per phrase, than captiveT. g. guttatamales from Timor. In contrast to the differences betweenT. g. castanotisandT. g. guttata, little geographic variation was found withinT. g. guttataon the four islands studied, although there was a cline of decreasing size in bill depth from west (Lombok) to east (Timor). The status of the two forms,T. g. guttataandT. g. castanotis, is discussed.