Twenty-three hydroquinone and quinone derivatives were assayed for antimicrobial effects and brine shrimp and fish lethalities, to establish relevant structure-activity relationships (SAR). Linear 2-prenyl-1,4-hydroquinones used for bioassay were obtained either by isolation from the sponge Ircinia spinosula or by synthesis. Corresponding quinones, as well as hydroquinones possessing saturated side-chains composed of one to eight isopentane units, were also synthesized and biologically evaluated. Terpenoid 1,4-benzoquinones displayed moderate antimicrobial activity against three microorganisms, SAR studies indicate the optimum length of the side-chain is in the range of five to fifteen carbon atoms.