Zimmerius villarejoi (Mishana Tyrannulet) is the second novel species to be described in recent years from poorly drained, white sand varillal forest near Iquitos, Depto. Loreto, Peru. It was initially detected by its vocalizations. Although well differentiated, close parallels in plumage and bill color suggest that Z. villarejoi may be most closely related to the poorly known and considerably larger Z. cinereicapillus (Red-billed Tyrannulet), with which it appears to be elevationally parapatric or allopatric. Amazonian forests growing on white sand and other nutrient poor soils hold many ornithological surprises and merit increased attention in field inventories.