The invention relates to novel compounds of the type of the imidazolidines of the formula I ##STR00001## in which R1 to R7 are as defined in the claims.They are used for preparing a medicament for the treatment or prophylaxis of the central nervous system, of lipid metabolism, of infection by ectoparasites, of disorders of gall function and for improving the respiratory drive and are therefore used for treating respiratory distress.Additionally, the compounds increase the muscle tone of the upper respiratory tract, thus suppressing snoring.