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-2-acetamide-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. Aplysinolide [1] was assigned formula C₁₁H₁₀O₃Br₂ based on mass spectral data. The structure 1 was assigned based on spectral data and nOe observations. Aplysinimine [2] was assigned formula C₉H₉NO₂Br₂ based on mass spectral data and spectral comparisons with synthetic analogs. Aplysinketal A [3]'s structure was confirmed by X-ray crystallography. Aplysinketal B [4]'s structure was assigned by analogy with 3. The isolation of aplysinimine [2] is remarkable as a possible precursor of other bromo-compounds. Aplysinolide [1] has an unusual α,β-unsaturated side chain. The new mixed ketals 3 and 4 are likely natural products. All natural products isolated were tested for antibacterial activity; the new bromo-compounds were inactive.