During the large-scale isolation of the batzelladines A and B, which are inhibitors of gp120-CD4 binding, we isolated 19 minor guanidine alkaloids. As part of our search for biologically active natural products, we examined the minor fractions obtained during a scale-up of the batzelladines A-E. One of the non-polar fractions of an extract from the sponge Batzella sp., which eluted from a Si gel column using MeOH-CH2Cl2, was subjected to extensive Si gel preparative TLC using unusual combinations of solvent systems. This fraction afforded ptilocaulin (1), isoptilocaulin, 8b-hydroxyptilocaulin, three new tricyclic guanidine alkaloids named 8a,8b-dehydroptilocaulin (2), 8a,8b-dehydro-8-hydroxyptilocaulin (3), and 1,8a;8b,3a-didehydro-8-hydroxyptilocaulin (5), and the recently described mirabilin B (4). The structures and relative stereochemistry of these compounds were determined by spectral analysis and by comparison with spectral data of ptilocaulin (1).