  To solve the puzzle of metamagnetic phenomena in heavy fermion systems, we
have compared paramagnetic isostructural Ce and Yb systems, CeNi$_2$Ge$_2$ and
YbNi$_2$Ge$_2$, both of which are located near a magnetic instability. The most
intriguing result is discovery of a metamagnetic-like transition in both
systems from magnetization measurements in a pulsed magnetic fields. This is
the first observation of the metamagnetism for isomorphic Ce and Yb
paramagnetic systems. Similar to other metamagnets, the metamagnetic transition
fields for both compounds are well scaled by the temperature $T_{\chi}^{\rm
max}$, at which the magnetic susceptibility shows a maximum. In addition, for
CeNi$_2$Ge$_2$ a peak of nonlinear susceptibility $\chi_3$ appears at
approximately $T_{\chi}^{\rm max}/2$, as for other heavy-fermion metamagnets.
In contrast, YbNi$_2$Ge$_2$ shows only a sign change for $\chi_3$ at
$T_{\chi}^{\rm max}$, as observed in itinerant metamagnets located near the
ferromagnetic critical point. The metamagnetism of CeNi$_2$Ge$_2$ corresponds
to a typical Kondo lattice system, whereas that of YbNi$_2$Ge$_2$ is similar to
the nearly ferromagnetic itinerant systems. Other possibilities for the
metamagnetic behavior of YbNi$_2$Ge$_2$ are also discussed.
