Starting from the words of Paracelsus, 'allein und fremd und anders'--alone and foreign and different--the influence of this important Swiss physician for the balneology of his time is outlined. Up to our days Paracelsus is honored as the real father of balneology, whereas other authors saw and probably still see hypotheses and in part utopias in his specific ideas. Paracelsus has described quite a number of thermal springs in Switzerland, Austria and southern Germany, some of them rather in detail. It is certainly questionable that he visited all of them personally. Bad Pfäfers, however, definitely belongs to them, since undoubted testimonies exist that emerged during his life time. His famous 'Baderbüchlin', though, has been printed after his death in 1562. His theoretical ideas about the effects of bathing are in part very modern, others originate from medieval alchemistic sources. He used this theory of 'Separatio' of the three basal elements sulphur, mercurius and sal, as well as the idea of the 'light of Nature', but beyond that he discussed also influences of personified forces, which he assumed in nymphs, melusins and others. Furthermore, in his balneology he expressed clearly his doctrine about the macro- and microcosmic relation, and he used in his balneotherapy vegetable and mineral compounds up to precious stones. Time, too, had a special importance for the effectiveness of the bath in his eyes.(ABSTRACT TRUNCATED AT 250 WORDS)