The pigments showing fluorescence maxima at 390, 366, 450-460 and 520 nm at excitation wavelength 254, 366 and 450 nm respectively, were detected in the cells and culture media of the obligate methylotroph Methylomonas Pl1 and facultative methylotroph Pseudomonas J26. The maximum at 520 nm is associated with the occurrence of a flavin pigment enabling growth of Lactobacillus casei E ATCC-7469 on the vitamin B2 deficient medium. The remaining fluorescence maxima are related to the prosthetic group of methanol dehydrogenase.