The first evidence that the infrared properties of galaxies were affected by the presence of bars was presented by Hawarden et al. (1986), who showed that a number of barred galaxies exhibit an energy distribution that is characterized by high 25 µm / 12 µm and low 100 µm / 25 µm flux density ratios. They estimated that over 30% of barred luminous galaxies show a flux excess at 25 µm and attributed this excess flux to a circumnuclear region of intense star formation.
The sample analyzed by Hawarden et al. includes only galaxies that have 12 µm and 25 µm flux densities above the IRAS point source catalog limit. Devereux (1986) has examined the effect of bars in the somewhat larger volume-selected sample of galaxies that was defined in section 3. He finds that the effect of bars is much more important in early-type galaxies than in late-type galaxies. He finds that most of the early-type galaxies exhibiting high compactness are barred, as are 29 of the 35 galaxies in the ``hot'' and ``early'' class in Table 1. This work is described in more detail elsewhere in this volume.
On a smaller scale, aperture synthesis observations in the 2.6 mm CO line have provided evidence for bar-like structures of molecular material in the inner regions of IC 342 (Lo et al. 1984) and NGC 6946 (Ball et al. 1985).