MicroRNAs are major regulators of gene expression at the posttranscriptional level. Besides being detected intracellularly, microRNAs have been found in body fluids, as well. Circulating microRNAs may have hormone like features, since they might affect distant cells as mediators of intercellular communication. MicroRNAs occurring in serum, urine, stool and saliva can be exploited as biomarkers of several diseases, and intensive research efforts are being performed in this field. MicroRNAs are also found in breast milk, and it cannot be excluded that these may act on the baby as a form of inter-individual transfer of epigenetic information. The presence of food-derived microRNAs is even more astonishing, thus plant microRNAs have been detected in the circulation, and these could be functionally active in the human/animal organism. Based on these observations, microRNAs could be involved in the transfer of gene expressional/epigenetic information between different individuals, but also between different species, even cross-kingdom. This microRNA-mediated communication might alter our concepts on the functioning of nature and on the development of diseases, as well.