Pestalazines A (1) and B (2), two new diketopiperazine heterodimers, and pestalamides A-C (3-5), three new amides, have been isolated from cultures of the plant pathogenic fungus Pestalotiopsis theae. The structures of these compounds were elucidated mainly by NMR spectroscopy. The absolute configurations of 1 and 2 were determined using Marfey's method on their acid hydrolysates and by comparison of their CD spectra with that of a model compound. Compounds 1, 3, and 6 displayed inhibitory effects on HIV-1 replication in C8166 cells. Compound 3 also showed potent antifungal activity against Aspergillus fumigatus.