[Critical review of our knowledge and presentation of a new working hypothesis concerning the stability of the precorneal tear film (PCTF) (author's transl)].

1. The paper reviews critically our present knowledge and experimental findings concerning the structure, formation and stability of the PCTF. 2. A new hypothesis, which contradicts Holly's concept, is put forward to explain the rupture of the PCTF (formation of dry spots). 3. Special chapters deal with tear secretion and drainage, and finally with the function of the eyelids (blinking), especially in relation to the formation and preservation of a stable preocular tear film.