Confocal interference reflectance contrast imaging (IRM). Transmitted light DIC (left), single-wavelength (488-nm) IRM (middle), and dual-wavelength (488-nm, 633-nm) IRM (right) images of living fibroblasts from dissociated embryonic quail heart tissue growing on a glass substrate. In the IRM images, the contrast arises from interference between the laser light reflected from two surfaces (e.g., basal-cell membrane and glass substrate). The image was acquired at full aperture with a 63X (NA = 1.2) water-immersion objective, but the high degree of coherence of the illuminating laser light nevertheless causes the higher-order fringes (e.g., from interference between reflections off the apical and basal-cell membranes) to have much higher contrast than with conventional illumination (Izzard and Lochner 1976; Sato et al. 1990). The dual-wavelength IRM image is quite useful for discriminating between the zero-order (black) fringes, which occur at the same location for both wavelengths, and first- or higher-order (green, yellow, red) interference bands, which occur at different positions for the two laser lines. (Specimen kindly provided by Dr. Jean Sanger, Upstate Medical University, SUNY Syracuse.)