The importance of probiotic-containing products for maintaining health and well-being is becoming a key factor affecting consumer choice, resulting in rapid growth and expansion of the market for such products, in addition to increased commercial interest in exploiting their proposed health attributes. The majority of probiotic foods already in the market, such as fermented milk and yogurt are fresh products and are generally consumed within days or weeks of manufacture. In contrast, hard cheeses, such as Cheddar have long ripening times of up to two years. Cheddar cheese may offer certain advantages over yogurt-type products in terms of delivery of viable probiotics, such as the reduced acidity of the cheese compared to yogurt environments and the high fat content and texture of Cheddar cheese may offer protection to the microorganisms during passage through the gastrointestinal tract (GIT). Indeed, previous studies have demonstrated that Bifidobacteria survive well in both Cheddar and Gouda cheeses. Our studies have involved the incorporation of a number of probiotic Lactobacillus strains into Cheddar cheese and assessment of their performance during ripening (Gardiner et al., 1998). These strains had previously been isolated from human upper GIT during surgery. These studies demonstrated that two Lb. paracasei strains grow and sustain high viability in cheese while Lb. salivarius strains die during the ripening period. Consequently, probiotic Cheddar cheeses can be manufactured containing high levels of Lb. paracasei strains (108 cfu g-1 cheese) at a relatively low cost to the producer and using identical make procedures. Importantly, our studies show that incorporation of these strains does not impact negatively on cheese quality, including aroma, flavour and texture. In addition, preliminary results suggest that cheese also compares very favourably with yogurt regarding delivery of viable cells to the GIT despite the apparent age difference of the products.