The diffuse sky emission in 7 spectral bands between 2 and 4.6 microns has been observed with a cooled balloon-borne IR telescope (TRIP). The results, reported here, confirm state-of-the-art atmospheric models for the continuum emission lambda > 3 mu m and for the OH component at lambda < 2.3 mu m. On the other hand, excess flux in the 2.3 to 2.5 mu m atmospheric window is found at a level of lambda I-lambda similar or equal to 1.5 - 2 10(-10) W cm(-2) sr(-1). Given its modulation with the zenith angle, this signal can be attributed to residual atmospheric emission, possibly due to narrow saturated absorption lines. The sky brightness detected by TRIP in the atmospheric window is 1.5 magnitude fainter at balloon altitudes than the typical sky brightness at South Pole. However, in optimal atmospheric conditions, the sky brightness at South Pole can be only half a magnitude brighter.
