In addition to known bromo-compounds 5-11, the new brominated metabolites aplysinolide [1], aplysinimine [2] and two mixed ketals, aplysinketal A {3} and aplysinketal B [4], have been isolated from the sponge Aplysina (Verongia) thiona. Their structures were determined by spectroscopic methods. In addition, an X-ray analysis of compound 3 was performed.Sponges of the order Verongida have yielded a wide variety of brominated compounds with suggested 3,5-dibromotyrosine origin (1). 2,6-Dibromo-4-acetamide-4hydroxycyclohexadienone [5] (2), the hydroxydienoic methyl ester 6 (2), and aeroplysinine 1 [7} (3) were responsible for the antimicrobial activity of the MeOH extract of Aplysina thiona De Laubenfels, a tropical Eastern Pacific sponge of the family Aplysinidae, order Verongida, collected at Puerto Escondido Bay in Oaxaca, Mexico.Aeroplysinine 2 [8} (4), 3,5-dibromo-2-hydroxy-4-methoxyphenylacetamide [9} (5), the hydroxydienoic acid 10 (2), and the bis-oxazolidone derivative 11 (6) were other known constituents isolated from this sponge.The hydroxydienoic methyl ester 6 and the hydroxydienoic acid 10, previously obtained by synthesis from the dienone 5 and the dimethoxyketal 12, respectively (2), have now been isolated from this sponge as natural products. Besides the brominated compounds, ß-sitosterol was obtained from A. thiona.Aplysinolide [1] was assigned formula C12H10O3Br2 based on mass spectral data, which indicated the presence of two bromine atoms (molecular ion cluster at mlz 360, 362, 364) as well as fragments corresponding to the successive loss of Me, HCO, and 43 mass units. The ir spectrum exhibited a band for a carbonyl function (1780 cm-1), while the 'H-nmr spectrum at 400 MHz showed two broad singlets at 2.39 and 2.59, indicating the presence of two geminal vinyl methyl groups, a singlet ( 3.92) for a methoxyl group, and a singlet ( 7.65) for one aromatic proton in a pentasubstituted benzene ring.