and York 1992; Steidel 1994). Whether DLA are proto-spirals or proto-dwarfs can be indicated by their observed abundance pattern. To this purpose in this paper we will present models of chemical evolution for galaxies of different morphological type and compare them with the observed abundances in DLA.

Observed abundances in damped Ly$\alpha$ systems
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So far chemical abundances have been measured in a set of DLA systems and with a variety of resolutions and accuracies by Black et al. (1987), Meyer & York (1987), Chaffee et al. (1988), Meyer et al. (1989), Meyer & Roth (1990), Rauch et al. (1990), Pettini et al. (1990), Meyer & York (1992), Pettini et al. (1994), Fan & Tytler (1994), Wolfe et al. (1994), Pettini et al. (1995), Lu et al. (1995a), Steidel et al. (1995), Lu et al (1995b). Here, we would like to focus on the abundances which could be used to compare with chemical evolution models and in particular with the few nitrogen detections so far reported in the literature. A summary of the abundances for the systems for which nitrogen detection or upper limits are available are reported in Table 1 and 2. All the original abundances have been renormalized 