Abstract
We present the first 2 mm spectral line survey of an extragalactic source, the nucleus of the starburst galaxy NGC 253. The survey covers the range from 129 to 172 GHz. We detected emission from 7 species not previously observed outside the Milky Way. One of the most outstanding result is the detection of NO with a relatively large fractional abundance of a few 10(-7). We discuss the origin of the chemistry in the nucleus of NGC 253 by comparing the measured abundances with those in prototypical galactic sources. We propose that the molecular abundances in NGC 253 are consistent with a chemistry dominated by large scale shocks.