Many diseases of humans are rodent-borne (leptospirosis, babesiosis, tularemia, rhickettsiosis). More recently, epidemics based on Hantaan virus have been described which caused cases of death in 10 to 25% of infected people. Keeping rodents away from human dwellings is for many rodent-borne diseases the most effective precaution for the restriction of their spreading. In terms of the Hantaan virus this is currently the only way to fight this virus. Reproduction and dispersal of rodents are the main factors affecting the spreading of rodent-borne diseases. Understanding the social mechanisms underlying population growth and dispersal of rodent individuals will enable us to develop biological methods to control these parameters. To achieve this, we focus our project on the elucidation of social factors affecting reproduction and dispersal of rodents in relation to the immune system of individuals. In the first part of our experiment we will investigate hierarchical structures among female voles which might lead to the inhibition of reproduction in suppressive females which consider to be one potential of dispersing rodents. The endocrine source for this suppression in relation to the immune response of these females will be investigated in more detail. The second part of our experiments will concentrate on the impact of conspecific odours on the sexual maturation of juvenile females which supposed to be another potential of dispersing individuals. Odour sources of conspecific adult females (urine) will be analysed chemically to determine those substances in the urine which are responsible for the observed effect on the maturation af juvenile females. In the third part the impact of various odour cues on the dispersal of those females which supposed to be the main carriers of rodent dispersal (submissive adult and immature juvenile females) will be studied. The synthesis of all data gathered on reproduction, maturation, social and endocrine status as well as the immune resistance of potentially dispersing individuals will allow conclusions on the social basis of dispersal in rodent populations and the possible use af olfactory factors to control these parameters by environmentally sound methods.