Strain UCMF(T) (T = type strain) was isolated from the conjunctiva of a European starling (Sturnus vulgaris) with conjunctivitis. Colonies grown on conventional mycoplasma agar possessed the typical fried-egg appearance observed with many mycoplasmal species. Electron micrographs of ultrathin sections of UCMF(T) revealed a pleomorphic cellular morphology; the cells ranged from spherical to elliptical or flask shaped. The cell size ranged from 0.3 to 0.5 microns. Strain UCMF(T) grows well in a variety of mycoplasma broth formulations at 25 degrees C, with rapid and heavy growth at 37 degrees C. No growth occurs at 42 degrees C. This organism ferments glucose but does not hydrolyze urea or arginine and has an absolute requirement for sterol from growth. Strain UCMF(T) does not hemagglutinate or hemadsorb chicken erythrocytes. The genome size is 870 kbp, and the guanine-plus-cytosine content is 31 mol%. Sequence analysis of the 16S rRNA gene demonstrated that this organism is unique and has not been described previously. Serological analysis confirmed that strain UCMF(T) is distinct from all previously identified Mycoplasma, Acholeplasma, Spiroplasma, Entomoplasma, and Mesoplasma species. This organism represents a new species, for which we propose the name Mycoplasma sturni. Strain UCMF (= ATCC 51945) is the type strain of M. sturni sp. nov.