In a long-term field experiment survival and development of all Ixodes ricinus stages were studied (both unfed and engorged and placed in cages at various altitudes). The main factors of the microclimate (temperature and relative humidity) were measured continuously. The experiment shows that the vertical distribution of I. ricinus is dependent on the character of the local microclimate (air layers near the ground surface) and its changes. This is the theoretical explanation of the upper limit of I. ricinus distribution in Central Europe (700 m a.s.l.) which had previously been set only empirically. The ticks (especially engorged females) introduced into higher altitudes by their hosts can survive there for a relatively long time and sometimes even oviposit, but they cannot give rise to a new local population.