A simple and multipurpose screening method was devised by taking advantage of the antagonism of cholesterol against the fungicidal activity of polyene antifungal antibiotics (PAA)¹}. Enactin (EN), formerly designated as H 646-SY3 substance²), and neoenactin (NE)³~⁵) are antimycotic antibiotics discovered by this screening as potentiators for PAA. Besides ability to potentiate the antimycotic activity of PAA, EN and NE share the common structural features, releasing L-serine by acid hydrolysis and showing positive FeCl₃ reaction. Later, NE was found to be composed of several congeners and the structures of the main component NE-A and the minor components NE-Bl₅ -B2, -Ml and -M2 were elucidated as shown in Fig. 1⁶~⁸). These NE congeners contain L-serine to form the hydroxamic acid structure. Therefore, we proposed the group name "hydroxamic acid antimycotic antibiotics (HAAA)" for EN, NE and the related antibiotics⁹~ ¹³). Like NE, EN is a complex of several congeners which are more hydrophilic and less active against Candida albicans Yu 1200 as compared with the NE congeners. In this paper, the purification and physico-chemical properties of the EN congeners are concerned.