Toxicity, antineoplastic, coagulant and anticoagulant effects of the following 22 Minnesotan aquatic plants were evaluated in terms of pharmacological properties: Anacharis canadensis, Calla polustris, Carex lacustris, Ceratophyllum demersum, Chara vulgaris, Eleocharis smallii, Lemna minor, Myriophyllum exalbescens, Nuphar variegatum, Nymphaea tuberosa, Potamogeton amplifolius, P. natans, P. pectinatus, P. richardsonu, P. zosteriformis, Sagittaria cuneata, S. latifolia, Sparganium eurycarpum, S. fluctuans, Typha angustifolia, Vallisneria americana, and Zizania aquetica. Toxicity of skellysolve F, chloroform, 80% ethanol and water extracts of these aquatic plants were evaluated in a number of animal experiments in Swiss Webster mice. Antineoplastic experiments involved amelanoma tumor cells. In vivo prothrombin time (PT) and partial thromboplastin time (PTT) were assayed in anti-coagulation experiments. The toxicity of the aquatic plants in general was found to be relatively low. The LD50 for the most toxic one, i.e., N. tuberosa (stem), in mice was 3 gm of dry plant material/kg (ca. 25.4 gm of wet plant material/kg). Only Nuphar variegatum indicated an anticancer possibility. The most significant increase of partial thromboplastin time (more than 20 minutes) was observed in Carex lacustris, Myriophyllum exalbescens, Nuphar variegatum and Nymphaea tuberosa.