The cultivation of Mycoplasma synoviae (MS) on growth medium requires supplementation with B-nicotinamide adenine dinucleotide (NAD), an expensive and relatively unstable compound. Strains of MS were adapted (selected) to grow in a medium supplemented instead with nicotinamide, a stable and inexpensive substance that can be heat-sterilized in the medium without impairing its growth-promoting properties. MS plate agglutinating antigens grown in nicotinamide-enriched media were comparable in yield and serological reaction to antigens grown with NAD supplementation.