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-Dibromoacetamide-4-hydroxycyclohexadienone [5] (2), the hydroxydienoic methyl ester 6 (2), and aeroplysinine 1 (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, β-sitosterol was obtained from A. thiona.