Aim was to investigate the efficacy of heat treatment on microbiological and biochemical quality of ass's milk and its effects on the growth of 4 different strains of Lactobacillus rhamnosus. Milk samples were obtained from 6 machine-milked asses (Martina Franca breed). Low bacterial counts (about 4 x 10(4) CFU/mL) were observed in raw milk samples likely due to high levels of lysozyme. The possible role of lysozyme was also suggested by stable pH values during storage for 15 days. Moreover, ass's milk demonstrated to be a good growth medium for potentially probiotic strains of L. rhamnosus since pH ranged between 3.67 and 3.85 for all the tested strains after a 48-hour period of incubation. Values were stable up to the end of the trials. Results evidenced that ass's milk is indeed an excellent candidate for probiotic beverages.