This study was conducted to define the characteristics of the uterus of reproductively failed pigs by transcutaneous ultrasonography (SONO) in order to investigate the appropriateness of SONO to diagnose presumptive uterine disorders. Zearalenone (ZEA) is known to affect uterine function and causes endometrial liquid accumulation and was also determined. In 33 sows and 14 gilts, of unknown reproductive stages and culled for failing to conceive, the uterus was scanned transcutaneously and the females slaughtered on the same day or the day after scanning. Parameters determined by SONO were uterine echotexture (UET; graded 1 for homogeneous to 4 for highly heterogeneous), uterine size (US; expressed as the mean sectional area of two to three cross-sections of the uterine horns given in cm2) and intrauterine content. Post mortem, the ovarian structures were assessed and females grouped accordingly into those in estrus (n=2), early diestrus (n=14), diestrus (n=15), late diestrus (n=1), anestrus (n=10) and having polycystic ovarian degeneration (n=5). The uterine weight (UW) was recorded and uterine specimens microscopically evaluated for an endometrial oedema (EO; grades 1 for none, to 4, if an oedema was clearly evident) and for immune cells to assess endometritis. Total ZEA was analysed in bile and females with >or=50 ng/ml judged as positive. The uterus could be examined in all animals. UET, US, UW and EO was found to be different between groups, and a positive correlation (P<0.001) established for US and UET (r=0.71), US and EO (r=0.51), UET and EO (r=0.57), US and UW (UW=357.6 x US(0.801); r=0.88). One female had intrauterine fluid and an acute-chronic endometritis diagnosed. Almost all females had a chronic endometritis and a majority found ZEA positive. No differences were observed between groups and a relationship between ZEA or chronic endometritis and UET, US, UW and EO were not established. In conclusion, transcutaneous SONO is appropriate to examine the uterus in reproductively failed pigs on farms, and the estimation of UET and US gives information on EO and UW. Intrauterine fluid is indicative for a severe uterine inflammation. Since groups differed in UET and US, but were equally ZEA positive and the uteri chronically inflamed, an UET and US specifically associated with ZEA or chronic endometritis is questioned.