A detailed analysis of the secondary metabolites of the Verongida sponge Aplysimz fistularis formafulva has been performed. Twelve bromotyrosine derivatives have been identified, of which two, 14 and 15, are novel compounds. Structure determination of compounds 14 and 15, performed by spectroscopic means, resulted in revision of the I3C-nmr assignments of aerothionine 111 and its derivatives. The sponge also elaborates an unusual imidazotetrahydropyrimidine derivative [16], probably derived from histidine, which has not yet been described as a naturally occurring compound.