Attenuated Salmonella enterica serovar Typhimurium MGN707, expressing the SzP protective protein of the MB9 serovar of Streptococcus equi subspecies zooepidemicus (SzP-MB9) was tested for its safety and efficacy as a nebulised intranasal vaccine against streptococcal uterine infections in mares. In a preliminary study, vaccinated mares (n=5) displayed serum, nasal and uterine responses (P<0.05) to S. Typhimurium lipopolysaccharide (St-LPS). Subsequently, vaccinated mares (expressor group, n=7), but not mares vaccinated with the vector only (control group, n=7), displayed significant increases in SzP-MB9 antibodies in serum, nasal and uterine washes (P<0.05). Assuming the uteri of all nine mares were free of streptococci prior to challenge with 6.3 x 10(9) colony forming units of S. e. zooepidemicus MB9, significantly fewer S. e. zooepidemicus were cultured from the uterine flushings of expressor-vaccinated mares (n=4) compared to control-vaccinated mares (n=5) (P<0.001). The only adverse reaction to vaccination was nasal haemorrhage in one mare.