Description:
<jats:p>Gravitational micro-lensing can be used to obtain information 1) on the inner structure of active galactic nuclei and 2) on the distribution of compact masses in the range 10<jats:sup>−4</jats:sup> … 10<jats:sup>2</jats:sup> solar masses. A regular monitoring of the most promising candidates for micro-lensing should be carried out. The strongest candidate is the macro-lensed quasar 2237+030, for which we expect a change in the luminosity ratio between the images of about 5 per cent per year.</jats:p>