Proteomic analysis of bovine, caprine, buffalo, equine and camel milk highlighted significant interspecies differences. Camel milk was found to be devoid of beta-lactoglobulin, whereas beta-lactoglobulin was the major whey protein in bovine, buffalo, caprine, and equine milk. Five different isoforms of kappa-casein were found in camel milk, analogous to the micro-heterogeneity observed for bovine kappa-casein. Several spots observed in 2D-electrophoretograms of milk of all species could tentatively be identified as polypeptides arising from the enzymatic hydrolysis of caseins. The understanding gained from the proteomic comparison of these milks may be of relevance both in terms of identifying sources of hypoallergenic alternatives to bovine milk and detection of adulteration of milk samples and products.