same as those of the neutral species, suggesting that both form in the same slab of HI material. Extra contributions to the absorption from HII regions in this DLA are also constrained by the lack of detection of NII, resulting in NII/NI $<$ 0.4. Viceversa, Green et al. (1995) interpret the abundances of the DLA towards MC3 1331+170 invoking an extraordinary amount of ionized gas, namely six times the neutral gas, which makes rather uncertain the abundances of ionized species. Highly ionized gas in the form of SiIV and CIV is frequently observed in the DLA. Sometimes the highly ionized gas is found at the same velocities of the neutral one but often is found at different velocities and therefore is very probable that highly ionized gas arises either in regions disconnected from the neutral material, or in the interfaces between neutral material and the intergalactic medium.

Presence of dust will selectively deplete the elements observed in the gas phase. In the dense clouds in the Galaxy the interstellar depletion of Al and Fe can reach $\simeq$ 2 dex, that of Si $\approx$ 1 dex, while, on the other extreme the O depletion is $\le$ 0.4 dex, that of N 