Loeffler Medium, a modified version of the 1887 Loeffler formula, is now called Loeffler Medium. Loeffler medium is a modified formula that Loeffler developed in 1887. It enhances primary and secondary isolation, and cultivates fastidious pathogenic microorganisms. After prolonged subculturing or prolonged incubation, Loeffler medium restores virulence as well as other identifying properties (microscopic/colonial). High serum levels are useful in determining organisms’ proteolytic activity. It can also be used to demonstrate pigmentation and ascospores.