  We have studied the muon decay energy spectrum from a sample of stopping muon
events acquired during the test run of the ICARUS T600 prototype. This detector
allows the spatial reconstruction of the events with fine granularity, hence
the precise measurement of the muon range and dE/dx with high sampling rate.
This information is used to compute the correction factors needed for the
calorimetric reconstruction. The Michel rho parameter is then measured by
comparison of the experimental and Monte Carlo simulated muon decay spectra,
obtaining rho = 0.72 +/- 0.06 (stat) +/- 0.08 (syst).
