  The existence of the Fundamental Plane of early-type galaxies implies that
the M/L ratios of early-types are well behaved. It provides therefore an
important tool to measure the evolution of the M/L ratio with redshift. These
measurements, in combination with measurements of the evolution of the
luminosity function, can be used to constrain the mass evolution of galaxies.
  We present the Fundamental Plane relation measured for galaxies in the rich
cluster CL 0024+16 at z=0.391. The galaxies satisfy a tight Fundamental Plane,
with relatively low scatter (15 %). The M/L is 31 +- 12 % lower than the M/L
measured in Coma, which is consistent with simple evolutionary models. Hence,
galaxies with very similar dynamical properties existed at a z=0.4.
  More, and deeper data are needed to measure the evolution of the slope and
the scatter of the Fundamental Plane to higher accuracy. Furthermore, data on
the richest nearby clusters would be valuable to test the hypothesis that the
Fundamental Plane is independent of cluster environment.
