After ad ministration of an oral dose to mice, hamycin, an antifungal antibiotic, penetrated the body tissues and eliminated Cryptococcus neoformans present in the lungs. Out of 11 polyenes (hamycin, aureofungin, trichomycin, etruscomycin, amphotericin B, pimaricin, mycostatin, candidin, candicidin, PA150, and filipin), hamycin and aureofungin showed the highest "in vitro" activity against Candida albicans. The antifungal activity of hamycin, PA150, and aureofungin was increased by the addition of serum, plasma, or crystalline albumins. This increase in activity can be used as an additional characteristic to differentiate some of the polyenes. We now believe that serum was responsible for our previous findings that "high concentrations of hamycin in the organs of mice were detected". It has been shown that the complete albumin molecule was required to increase the activity of hamycin. The possibility that serum globulins or other proteins may increase the hamycin activity is not ruled out by our experiments.