Because mycoplasmas are a diverse group of organisms and are difficult to culture, several different strategies for detecting mycoplasma contamination have been developed. To date, no one test is suitable for detecting all of the possible mycoplasmas that may contaminate hybridoma or myeloma cultures. Therefore, it is sensible to consider using several methods. The most commonly used techniques are described here. Mycoplasma screening by growth on microbial medium can be performed on agar plates or in broth culture. Cultures are grown under both aerobic and anaerobic conditions because some common strains of Mycoplasma prefer the lack of oxygen (Mycoplasma buccale, Mycoplasma faucium, M. orale, and M. salivarium). Mycoplasma colonies form a characteristic "fried egg" appearance on agar plates, and this is the diagnostic feature used to confirm mycoplasma contamination. The colonies are small and are most easily seen with an inverted microscope. A quicker method for testing for mycoplasma takes advantage of the DNA-intercalating dye Hoechst 33258. Fixed cells are stained with the dye, and contaminated cultures are detected by the bright, punctate cytoplasmic staining of the Mycoplasma DNA. Finally, commercial kits for the detection of mycoplasmas using colorimetric assays or reporter cells are also described.