Further investigations of the VLC (vacuum-liquid chromatography) fractions obtained from the dichloromethane solubles of the tropical marine sponge Cymbastela hooperi led to the isolation and characterization of five new diterpene formamides, 1-5. Compound 1 is one of the very few examples of a natural product that contains both formamide and isonitrile functionalities within the same molecule. In in vitro antiplasmodial bioassays, 1 was found to have moderate activity (IC(50) 0.5 microg/mL), 2 had weak activity (IC(50) 14.8 microg/mL), and 3-5 were inactive. The pattern of activity found for the metabolites investigated in the current study is consistent with previous findings for these classes of molecules.