Antifungal agents obtained from microorganisms have been known in the laboratory and tested in the clinic for more than a decade. A long list of now discarded antibiotics could be presented not only as evidence of the vast effort that has been expended but also as a measure of the resistance of human mycotic infections to specific therapy. The apparently simple fungi of the skin have also discouraged many chemists by appearing to be less affected by the extraordinarily powerful synthetic chemicals that were devised to destroy them than by Arthur Whitfield's hallowed mixture. Many workers, however, looked to antibiotics with renewed hope of destroying the organisms without harming the host. Progress has been made toward this goal in the management of yeast infections, but many of the mycoses remain intractable. The reasons for this are not yet apparent. As Ainsworth1 has pointed out: The