Dairy products such as cheese and yogurt are manufactured from pasteurised milk while in some cases sub-pasteurisation temperatures are employed for the former. Recent studies have shown increased survival of Mycobacterium avium subsp. paratuberculosis (Map) under such conditions. Therefore, the inactivation of this bacterium may rely on the manufacturing process or the product's intrinsic properties. Lactic acid bacteria (LAB) are known for their potential as inhibitors of food pathogens, a property exploited in their commercialisation as 'probiotic' products. The objective of this study was to investigate the in vitro inhibition of Map by probiotic strains and cheese LAB isolates. Supernatant from LAB cultured in de Man, Rogosa Sharpe broth was added to BACTEC 12B medium and inoculated with Map cells (approx. 10^4-5 cfu/ml). Growth index values were recorded regularly throughout a 10 wk incubation period. Sterile milk was co-inoculated with Map cells and 'probiotic' lactobacilli strains and incubated (35°C, 72h). The recovery of Map was monitored through the BACTEC radiometric method.Dilute supernatants from isolates identified as Lactobacillus casei (Danone) and the probiotic strain Lb. rhamnosus GG and a small number of cheese isolates prevented any increase in growth index values typical of Map metabolic activity. Map growth was inhibited (delayed) when supplemented with supernatants from a number of Lb. paracasei isolates. When co-inoculated with probiotic strains in sterile milk for 48 h (pH < 4.5) Map could not be detected by radiometric culture up to 50 days.The results of this study suggest the in vitro inhibitory effect of some lactobacilli on Map growth may be due to factors other than acid production. Irrespective of the mechanism of inhibition, the possibility exists for the inclusion of such strains in dairy products for the in situ inhibition of Map or furthermore their use as biotherapeutic agents in the gastro-intestinal tract.