Probiotics are defined as live micro-organisms, which when administered in adequate amounts, confer health benefits on the host. Scientists have isolated various strains of Lactobacilli from human milk (such as Lactobacillus fermentum and Lactobacillus salivarius), and the presence of these organisms is thought to be protective against breast infections, or mastitis. Trials of probiotics for treating mastitis in dairy cows have had mixed results: some successful and others unsuccessful. To date, only one trial of probiotics to treat mastitis in women and one trial to prevent mastitis have been published. Although trials of probiotics to prevent mastitis in breastfeeding women are still in progress, health professionals in Australia are receiving marketing of these products. High quality randomised controlled trials are needed to assess the effectiveness of probiotics for the prevention and/or treatment of mastitis.