This article is a short review of: a) development of theory on natural foci of communicable diseases in man, b) methodological approach to the investigation of natural foci, e.g. theoretical model in their investigation, and c) the use of theoretical model in the investigation of Lyme borreliosis. A great number of multidisciplinary studies on natural foci zooanthroponoses conducted through many years, in which ecological approach and numerous methods were applied, commencing from studies of the processes at the level of molecules, genes, cells, tissues, organismus, populations and species, contributed to the knowledge that epizootical process of natural foci of zooanthroponoses is almost an ideal natural model. Its investigation allows the establishment of the rules of epidemiological process which, for many reasons (ethical above all), is not accessible for experimental studies. On these principles a general block model has been worked out, which serves for the estimation of epidemiological manifestations of natural foci zooanthroponoses, and which, applied to Lyme borreliosis, enables the determination of active and potential foci and the estimation of the degree of risk of man infection in determined foci. Data obtained in such a way allow planning and application of adequate preventive measures.