The CHORUS Collaboration is presently building a new detector for the search of nu(mu)-nu(tau) oscillations on the CERN neutrino beam, this experiment being sensitive to a mixing angle an order of magnitude smaller than previous experiments. The basic components of the CHORUS ''hybrid'' detector are an active target made of nuclear emulsions (for the direct observation of the decay of tau-leptons), an air-core spectrometer with scintillating fiber tracking, a lead-scintillator (fibers and strips) calorimeter (with mu-tracking provided by planes of limited streamer tubes) and a muon spectrometer, consisting of iron toroids and drift chambers. We report here on the design of the calorimeter and on the tests performed on prototype modules
