Spectral properties of the intracellular pigments of flavpbacteroa were studied by "scanning" ultrasonic preparations, methanol extracts, MF preparations, slide cultures and whole cell suspensions. No genus-specific Amax were demonstrated with methanol extracts. In situ analyses of pigment, using ultrasonic preparations or whole cell suspensions, demonstrated that all strains of Flavobacterium spp. surveyed showed a discrete Amax between 418 and 421 nm. This peak was absent from scans of other yellow gram negative rods". Amplitude of Amax was accentuated by variation in incubation parameters. Good resolution was obtained by repositioning cuvettes in "conventional" spectrophotometers and attaching opal glass plates to the "detector suface" of cuvettes. The presence of a genus-specific Flavobacterium pigment, or pigment fraction, detected through in situ analysis, adds another feature to keys or schema used for characterization and identification of the organisms comprising this presently ill-defined taxon.