During the years 1994-1997, the emulsion target of the CHORUS detector was exposed to the Wide Band Neutrino Beam from the CERN-SPS. About 170 000 neutrino interactions were successfully located in the emulsion. Improvements in the automatic emulsion scanning systems and application of different criteria allowed the sample of located events to be used for studies of charm production. We present a measurement of the production rate of Do mesons based on a sample of 25 693 located nu(mu) charged-current (CC) interactions analysed so far. After reconstruction of the event topology in the vertex region, 283 D-0 decays were observed with an estimated background of 9.2 K-0 and Lambda decays. The ratio of cross-section of D-0 production and nu(mu) CC interactions is found to be (1.99 +/- 0.13(stat.) +/- 0.17(syst.)) x 10(-2) at 27 GeV average nu(mu) energy. (C) 2002 Elsevier Science B.V. All rights reserved.