  We present an analysis of the location of interacting E/S0 galaxies on the
Fundamental Plane (FP). Using the NEMO package, we performed N-body simulations
of close encounters and mergers of two self-gravitating spherical galaxies. Two
models for encounting galaxies - Plummer's and Hernquist's - were used. The
number of particles ranged from 20000 to 50000 per galaxy. The changes of
central density, half-mass radius and central velocity dispersion were
analysed. It was found that close encounters between galaxies alter noticeably
the above parameters within a very short time interval (10^7 - 10^8 years) just
before the final merger. The amplitudes of parameter changes strongly depend on
the initial mass concentration of a model. In some experiments we considered an
encounter of two spherical galaxies with dark matter components. The effect of
parameter changes was less pronounced than for the experiments without a dark
halo. The results of the simulations were used to discuss the FP for
interacting early-type galaxies.
