The opisthobranch molluscs are an incredibly diverse group of nearly exclusively marine organisms whose potent toxicity has made them ideal subjects for biotoxicology and biomedicinal studies. In fact, extracted toxins from various species of opisthobranchs have entered phase I and II clinical trials for the treatment of a variety of serious medical conditions. Some promising medicinal properties exhibited by these toxins include inflammation reduction, pain suppression, inhibition of fungal and bacterial growth, as well as potent anti-tumor and anti-cancer properties. In this study, 43 opisthobranchs from 11 different species of the suborders Nudibranchia (eight species), Sacoglossa (one specie) and Aplysiomorpha (two species) were collected from six sites along the Pacific Coast of Nicaragua during the summer of 2008 via SCUBA, snorkeling and tide-pool collections. Following species photo-documentation, the specimens were preserved in 100% acetone and brought back to the lab for species level identification and further analysis. In the lab, organic compounds were extracted for cytotoxicological analysis. To screen for potential anti-cancer properties, NIH 3T3 mouse fibroblast cells were exposed to high (500μg/L) and low (50μg/L) doses of the crude organic extracts for 24 hours. Following exposure, cytotoxicity was measured using an MTT assay. An ANOVA pairwise multiple comparison (holm-sidak) indicated that all but one of the ten species analyzed had a significant cytotoxic effect at the high concentration (P<0.001). Additionally, five were shown to have a significant cytotoxic effect at the low concentration as well (P<0.001). These results serve to identify target species for future investigations. Follow up research will be needed to isolate, purify and identify the specific chemical compounds responsible for the observed cytotoxic effects.