Three new cyclic peptides, microsclerodermins C - E (3-S), were isolated from two species of lithistid sponges from the Visayan Islands, Philippines. The sponge Theonella sp. contained peptides 3 and 4, while Mcnmleroderma sp. contained peptides 4 and 5. Their structures, which feature three unprecedented amino acids, were elucidated using spectroscopic methods and chemical degradation. 0 1998 Elsevier Science Ltd. All rights reserved.