The nudibranch Cadlina luteomarginata from San Diego, California, concentrates selected metabolites from the sponges that constitute its diet. Gut analyses revealed that C. luteomarginata consumes at least ten sponges although Axinella sp. and Myxilla incrustans are most frequently eaten. Field observations and analysis of metabolites suggest that keratose sponges Leiosella idia (= Spongia idia) and Dysidea amblia are also consumed. Three novel compounds, the furan 20, the isonitrile 23 and the isothiocyanate 24 were identified by analysis of spectral data. The secondary metabolites of C. luteomarginata were found only in the dorsum, which is exposed to potential predators. Five metabolites of C. luteomarginata were screened for antifeedant activity against fish and all showed some activity at 10-100 μg/mg in food pellets.