Seven diketopiperazines, corresponding to the cyclos (L)-Pro-(L)- Phe, (L)-Pro-Gly, (L)-Pro-( L)-Pro, (L)- Pro-(L)-Val, (L)-4-OH-Pro-(L)-Leu, (L)-4-OH-Pro-(L)- Phe, and (L)-Pro-(L)-Leu, were isolated from the Aspergillus fumigatus fermentation broth. The relative and absolute stereochemistries were determined on the basis of NOESY experiments and by using a modified version of Marfey's method using HPLC, respectively.166B14481453