  We show a systematic experimental study based on INDRA data of the stopping
power in central symmetric nuclear reactions. Total mass of the systems goes
from 80 to 400 nucleons while the incident energy range is from 12 AMeV to 100
AMeV. The role of isospin diffusion at 32 and 45 MeV/nucleon with 124,136Xe
projectiles on 112,124Sn targets performed at GANIL is also discussed. Results
suggest a strong memory of the entrance channel above 20 AMeV/A (nuclear
transparency) and, as such, constitute valuable tests of the microscopic
transport models.
