It has been known for about 20 years that our Galaxy has a radial abundance gradient as evidenced in the composition of stars and the ISM (see Pagel & Edmunds 1981 for discussion and references). The abundance gradient in the ISM is comparable to those measured in similar extragalactic systems and has become very well defined over the last few years (cf. Esteban & Peimbert 1995), but there was some doubt concerning the stellar abundance gradient (e.g., Gehren et al. 1985). The perceived difference between the Galactic abundance gradient as measured in the stars and as measured in the ISM has led to a considerable lack of confidence in our ability to accurately measure abundances. Fortunately, the situation has changed recently, due, in part, to one of our winter school participants. Smartt & Rolleston (1997) have shown that Galactic B stars do, in fact, show the same abundance gradient as measured in the ISM. This very important result should now lend credibility to future abundance work.
Nonetheless, some basic aspects of the systematic behavior of composition gradients in spiral galaxies remain poorly understood (see, for example, Vila-Costas & Edmunds 1992, VCE, and Zaritsky, Kennicutt & Huchra 1994, ZKH). Among these is the question of the differences in gradients among galaxies and the correlation of gradients with the structural properties of galaxies. Abundances in spiral galaxies have been determined to correlate with Hubble type, galaxy luminosity, and maximum circular velocity (e.g., Pagel & Edmunds 1981, McCall 1982, Garnett & Shields 1987, VCE, Oey & Kennicutt 1993, ZKH), although since these parameters correlate with each other, the fundamental correlation is as yet unclear (Garnett & Shields 1987, ZKH). It is still true that most spirals included in these studies typically include only a handful of observed HII regions, and this can lead to biases (Garnett & Shields 1987; ZKH; Kennicutt & Garnett 1996). For example, Kennicutt & Garnett (1996), from a spectroscopic sample of 40 HII regions in M101, discovered an asymmetry in derived abundances across that galaxy, which had not been noticed in previous studies using smaller HII region samples. Thus, detailed spectroscopic studies of large samples of HII regions in spirals are still needed to improve the galaxy comparisons.
Recently, Garnett et al. (1997b) have produced a detailed study of NGC 2403. I will use this study to highlight some of the important topics in spiral galaxy abundance studies. NGC 2403 is a nearby spiral galaxy of Hubble type SAB(s)cd (de Vaucouleurs et al. 1991; RC3) in the M81 group of galaxies. NGC 2403 is a morphological twin to the well studied Local Group Scd spiral M33, and, therefore, comparisons between the two galaxies are of interest. Both galaxies also have favorable inclinations, allowing good observations of both the contents of the disks and the internal dynamics.