Use of hair tubes and hair characterization of the Red-Bellied Squirrel Callosciurus erythraeus. The Asiatic Red-Bellied Squirrel has been introduced into the Pampas Region, where a wild population has now been established and is colonizing new areas. Hair tubes have been successfully used to assess the presence/absence of other species of squirrel through the identification of the collected hairs. The objectives of this study were to characterize the hairs of the Red-Bellied Squirrel and to test the use of hair tubes to detect the presence of this species. The study was conducted in the province of Buenos Aires, Argentina, from January to July 2004. Hairs from the back, head and tail have dark and light stripes while hairs from the belly are uniformly reddish brown. A multi-seriated medullar pattern was observed in the hairs of the back, head and belly, while the tail’s hairs showed a different medullar pattern that can be described as overlapped dark rings. Cuticle scales patterns corresponded to the normal mosaic type in the hairs of the tail, back, head and belly, and for the last three regions a different pattern was observed next to the hair bulb. Hair tubes were made of PVC tubes (25 × 6 cm) opened at both extremes. The tubes had an adhesive tape attached at both extremes and bait (peanuts and nuts) was offered in the centre. Given the arboreal habits of this squirrel, traps were placed on tree branches and inspected weekly. The hair tubes were successful in collecting hairs of the Red-Bellied Squirrel that can be distinguished from those of other mammals inhabiting the same area. Because this is quite a simple and inexpensive technique, we consider it an appropriate method to evaluate the presence of this alien species in the region.