Faculty of Veterinary Medicine, LAMOFOPA, PPGCV, State University of Ceara, Fortaleza, CE, Brazil Institute for Research and Technology, Tiradentes University, Aracaju, SE, Brazil Nucleus of Biotechnology Applied to Ovarian Follicle Development, Federal University of São Francisco Valley, Petrolina, PE, Brazil Laboratory of Ultrastructure, CPqAM/Fiocruz, Federal University of Pernambuco, Recife, PE, Brazil Biotecnology Nucleus of Sobral (NUBIS), Federal University of Ceara, Sobral, CE, BrazilNational Council for Scientific and Technological Development (CNPq), and the Coordination for the Improvement of Higher Education Personnel (CAPES), and the Brazilian Innovation Agency (FINEP) and the Ceara State Foundation for the Support of Scientific and Technological Development (FUNCAP). Juliana Jales de Hollanda Celestino is a recipient of a grant from FUNCAP.This study investigates steady-state level of bone morphogenetic protein-15 (BMP-15) mRNA in caprine follicles, and the effects of BMP-15 on in vitro development of preantral follicles. Ovarian fragments were cultured for one or seven days in Minimal Essential Medium (MEM(+)) with BMP-15 (0, 1, 10, 50, 100 or 200 ng/mL), and further analyzed by histology, transmission electron and fluorescent microscopy. BMP-15 mRNA in secondary follicles was higher than in primordial and primary follicles. After seven days, 10, 50 or 100 ng/mL of BMP-15 maintained the percentage of normal follicles similar to the control (non-cultured), and increased the oocyte and follicle diameters when compared to the control and MEM(+). BMP-15 at 100 ng/mL increased the secondary follicles and maintained their ultrastructural integrity. In conclusion, the BMP-15 mRNAs were detected in all follicular categories. BMP-15 (100 ng/mL) maintained the integrity and promoted the growth of caprine preantral follicles cultured for seven days.2050-01-01