Compact slab repetitively-pulsed RF discharge overtone CO laser is developed. Results of parametric study of the laser with cryogenically cooled electrode system operating in sealed-off mode are reported. The average output power of the laser was up to 0.5 W with maximal efficiency of ~1.5 %. More than ~80 ro-vibrational overtone CO laser lines (summarizing two spectral ranges 2.5-3.1 μm and 3.1-4.2 μm corresponding to two sets of laser resonator mirrors used in the experiments) were observed. Start-up experiments on development the laser head of new design with enlarged active medium length (40 cm) were carried out. Preliminarily the output power of the overtone CO laser with the new laser head reached 0.75 W at the efficiency up to 1 %.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.