Autodetachment spectroscopy of a molecular anion has been demonstrated for the first time using a weak infrared diode laser. A low‐power (5 &mgr;W) laser beam overlaps a fast ion beam, driving an infrared vibrational‐rotational transition in a molecular anion. The vibrationally excited anion autodetaches, and the resulting fast neutral is detected. In the first demonstration of the new technique, a previously unmeasured transition in the fundamental (1←0) band of NH−was observed near 2806 cm−1with a signal‐to‐noise ratio of 15:1. There is reasonable agreement between calculated and observed signal strengths. Future instrumental improvements are expected to yield substantial improvement in sensitivity. The present experiment extends the range of applicability of autodetachment spectroscopy beyond the range of color‐center lasers. With straightforward improvements, the technique is applicable to a number of larger molecular anions having low electron affinity.