The aim of this study was to investigate the reproductive problems and determine the effect of treatment method on the pregnancy and foaling rates of 27 barren Arabian mares. The mares were examined over two study seasons. Ultrasonography and gynecological examinations were performed for all mares that were unable to conceive during the previous season and mares for which pregnancy was not achieved even after mating with stallions three times during each season. Endometrial swab samples were also obtained for microbiological examination. Cytology and endometrial biopsy samples were obtained from all mares in the first study season. Endometrial biopsy samples were also obtained from the mares in the second study season that were not pregnant at the end of the season due to the applied treatment. Klebsiella pneumoniae (42.9%) was the most frequently isolated species. A cytology score of >0 caused a decrease in the foaling rate (P < 0.07). A statistically significant decrease was observed in the pregnancy and foaling rate of mares in Category © > I (P < 0.05). Therefore, positive cytology and biopsy results should be considered prior to application of treatment in order to increase the expected foaling rate in barren Arabian mares.