It is difficult, indeed unwise, to engage in meaningful discussion on the pathogenesis of infectious diarrhea without first considering the basic nature of the systems that, when perturbed, give rise to the pathophysiological state of diarrhea. It is also true that, in some cases (eg, diarrhea caused by enteropathogenic Escherichia coli [EPEC]), a great deal is known about the detailed molecular biology of initial attachment and the induction of ensuing cytopathol-ogy, but very little is known about the pathophysiological correlates that give rise to disease. In other cases (eg, diarrhea caused by rotavirus), a great deal is known about the pathophysiological responses giving rise to the disease, but very little is known about the pathogenic mechanisms triggering those responses. This mini-review reflects these different emphases. It is also written from an experimental, not a human clinical, standpoint.