Ovine Johne's disease (OJD) is a significant cause of mortality of adult sheep in some parts of Australia and vaccination for sheep with OJD with Gudair^TM, a killed Mycobacterium paratuberculosis preparation, is being investigated as a disease control tool. This paper presents preliminary data on the impact of vaccination on faecal shedding of M. paratuberculosis (as assessed by pooled and individual faecal culture), mortality rate, lamb growth, condition score and wool productivity, vaccine injection site lesions and cellular (BOVIGAM^TM) and humoral (PARACHEK^TM) immunity. On each of three properties in New South Wales experiencing significant OJD losses (5 to 15% per annum), 200 Merino lambs (age 1-4 months) were vaccinated with Gudair^TM, and 200 lambs were sham vaccinated with saline (1 property in December 1999 and 2 in June 2000). Animal assessments and sample collections are being conducted twice yearly. Data to date indicates that Gudair^TM significantly delays faecal shedding for the first year post-vaccination (p.v.) and when shedding commences, it is at a significantly lower rate than unvaccinated animals. There have been no OJD attributable deaths in vaccinated sheep compared to 19 confirmed OJD mortalities in control sheep. No significant differences have been noted in live weight, condition score and wool productivity. Vaccine injection site lesions were detected in almost 50% of sheep at 2 months p.v., reducing to 10-30% by 2 years p.v. The vaccine stimulates both CMI and ELISA responses in a high proportion of vaccinated lambs which tends to decline over time, accompanied by a significant increase in the proportion of unvaccinated animals with positive immune reactions, presumably reflecting an increasing prevalence of OJD in this group. This data has been used to seek registration of Gudair^TM in Australia and it is expected that the vaccine will have an important role in OJD control in Australia.