Thresholds have been measured for the breakdown of helium by laser radiation near 3.8 &mgr;m in wavelength. Four‐&mgr;sec chemical laser pulses were focused to a well‐defined spot 100 &mgr;m in diameter. Values of the instantaneous irradianceqtand the accumulated fluenceetoccurring at time of breakdown were observed as a function of helium pressure in the range 0.12–0.99 atm. The measuredqtwas 2.3 ×1010W/cm2at 1 atm, in good agreement with results scaled from other wavelengths.