The growing usage of nanomaterials in a variety of industrial, consumer, and medical applications has spawned attempts to correlate in vitro nanomaterial characteristics to in vivo manifestations of toxicity. Cellular toxicity of nanomaterials, particularly reported relationships of surface area to toxicity, may be related primarily to surface-adsorbed species. Accordingly, we have observed pronounced in vitro macrophage response to lipopolysaccharide (LPS) in the presence of gold nanoparticles and increased zebrafish embryo toxicity to dissolved pollutants in the presence of carbon fullerenes and multiwalled nanotubes. These results suggest a strong link between nanomaterial handling/history and cellular toxicity.