The generation of "natural microbial products" which promote the barrier effect of the intestine and which are efficacious in the treatment of enteric infections, remains a critical target. To date, lactic acid bacteria have been the focus of much research and product development. Recent technical developments in molecular microbiology have identified other probiotic strains which may have greater potential for enhancing disease resistance. New research on the mechanisms of bacterial/ mucosal interactions will define their mode of action in the neonatal gut and provide a validation of the probiosis concept.