The aim of this study was to investigate whether unilateral, intraovarian infusions of bacteria might have induced morphological changes in the contralateral ovary. Eleven sexually matured gilts with controlled estrous cycle were used. The animals were randomly divided into two groups: I (Gr. I, treated; n = 4), and II (Gr. II, control; n = 7). In Gr. I, 1 ml of bacterial suspension (10(3) colony forming units/ml of saline of Escherichia coli, Staphylococcus aureus and Corynebacterium pyogenes, in proportion 1:1:1) was infused into the hilus of one ovary from the 15th to the 19th day of the estrous cycle. At the same time, 1 ml of saline was infused into the hilus of the contralateral ovary and into both ovaries of the control gilts. On the 7th day of the next cycle, the ovaries were dissected out. There were no significant differences in the number of follicles and corpora lutea (CL) as well as in weight and size between the bacteria-infused, contralateral and control ovaries. The microscopic observations of the bacteria-infused ovaries revealed the presence of focal infiltrations of neutrophils in the softened stroma, especially around dilated blood vessels filled with erythrocytes. In the contralateral ovaries, the number of regularly distributed neutrophils in the softened stroma was greater than that found in the bacteria-treated ovaries. CL of the bacteria-infused ovaries had more numerous, dilated blood vessels than CL observed in the contralateral gonads. More neutrophils were found in CL of both ovaries in Gr. I as compared to those observed in Gr. II. In Gr. II, single neutrophils were found also in the stroma where the tip of the cannula was inserted. This study revealed that in gilts, unilateral, intraovarian administration of bacteria did not change the number of ovarian structures, the weight and size of the bacteria-infused and contralateral ovary, but induced inflammatory changes in both ovaries.