Cytotoxic compounds, presumably functioning in defense against predators, parasites, and infectious organisms, are produced or sequestered by a variety of invertebrate animals. Marine sponges, in particular, have proven to be a rich source of these compounds, and many of the compounds or derivatives of them are valuable pharmaceutically. Preliminary work suggested that freshwater sponges may also harbor cytotoxic/ such compounds. In order to examine this possibility, I extracted specimens two species of freshwater sponges, Ephydatia muelleri and Spongilla lacustris, with a range of solvents and tested for cytotoxic activity using a brine shrimp survival assay. I confirmed that freshwater sponges contain cytotoxic activity and also began a characterization of the molecule (or molecules) responsible for this activity using partitioning, silica gel chromatography, and ultrafiltration. My results suggest that the active molecules are relatively polar and have molecular masses of 3000 - 30,000 Da.