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Among the surveys compiled in this review, those towards absorption systems deserve an special mention due to its enormous potential to carry out molecular studies at intermediate redshift. Such is the case of the spectral scan carried out with ATCA towards the absorption system PKS 1830-211 (Muller et al. 2011). The survey (see Invited talk in this volume by Sebastien Muller for an extensive description of the results) covered the frequency range from 30 to 50 GHz, equivalent to the 5-3 mm rest frame between 57 and 111 GHz at the redshift of z = 0.89. As a result of the spectral scan 28 molecular species and 8 isotopologues were identified. This study turns PKS 1830-211 into one of the extragalactic sources with the largest number of molecular detections. The accurate fractional abundances derived from these observations allows complete comparison with Galactic sources (see Fig. 8 in Muller et al. 2011) which showed the similar molecular composition between this absorption system and that found in typical Galactic diffuse and translucent clouds.