We have studied a novel cobalt cage surfactant which has significant in vivo biological activity on parasitic nematodes. This activity was investigated by the confocal microscopy of sheep red blood cells, allowing the mode of action to be studied at a cellular level. Surface force measurements were carried out using colloid probe atomic force microscopy on adsorbed bilayers of this surfactant, which were found to be mechanically weak. The surface properties of the surfactant were measured and correlated with its biological activity. The theory of membrane curvature was also used to describe the surfactants biological activity.