Objective: A novel approach for creating a soft cochleostomy has been described using a handheld CO 2 laser hollow waveguide from termed in the following the handheld CO 2 laser fiber. The effects on cochlear function have been studied in an animal model and were compared to the effects of the micro drill. Study Design: Combined human temporal bone and experimental animal study. Materials and Methods: Four human temporal bones were used to describe the technique to create a cochleostomy using the handheld CO 2 laser fiber. A cochleostomy was made by thinning the cochlear wall with a motorized drill and by creating an opening with the CO 2 laser fiber. Eighteen guinea pigs were used to investigate the effects of the CO 2 laser and the drill on cochlear function. An electrode was placed in the round window niche to measure compound action potentials (CAPs). Baseline cochlear function was determined by recording CAP thresholds evoked by acoustic tone pips and was re-assessed during and after a cochleostomy was made. The protocol was repeated using a diamond-burr drill technique. Results: The handheld CO 2 laser fiber is an ideal tool to create cochleostomies under 1 mm in diameter. In the guinea pig animal model, CAP thresholds showed little change after creating the cochleostomy at 4 W laser power setting and revealed focal threshold elevations averaging 32 dB at higher laser power settings. Conclusions: The human temporal bone study introduces a novel surgical approach for soft cochleostomies that uses both the drill and the CO 2 laser fiber. Threshold elevations, which were observed after making the cochleostomy with the laser, compared favorably to the diamond burr technique.