  We discuss some results of a morphological study of edge-on galaxies, based
on optical and especially near-infrared surface photometry. We find that the
vertical surface brightness distributions of galaxies are fitted very well by
exponential profiles, much better than by isothermal distributions. We find
that in general the vertical scale height increases when going outward. This
increase is strong for early-type spiral galaxies and very small for late
types. We argue that it can be due to the presence of thick discs with scale
lengths larger than the galaxy's main disc. Finally we discuss the
colour-magnitude relation in I-K for spiral galaxies. We find that it is a
tight relation, for which the scatter is similar to the observational
uncertainties, with a steeper slope than for elliptical galaxies.
