  It is demonstrated that the slope of the upper critical field
$|dH_{c2}/dT|_{T_{c}}$ in superconductors with $d$-wave pairing drops rather
fast with concentration of normal impurities, while in superconductors with
anisotropic $s$-wave pairing $|dH_{c2}/dT|_{T_{c}}$ grows, and in the limit of
strong disorder is described by the known dependences of the theory of
``dirty'' superconductors. This allows to use the measurements of $H_{c2}$ in
disordered superconductors to discriminate between these different types of
pairing in high-temperature and heavy-fermion superconductors.
