Radiation from Si-like Kr XXIII and Mo XXIX has been observed on the JET tokamak. In determining the ionization stages of the new transitions the temporal variation of the line intensities during discharges was investigated in detail. In the wavelength range 70­330Å, 11 new Kr XXIII and 11 new Mo XXIX lines were classified by means of isoelectronic analyses and comparisons with relativistic calculations. The results confirm and extend previous tokamak studies