Carbon nanotubes (CNTs) entered the domain of biological research a few years ago, creating a significant amount of interest due to their extraordinary physicochemical properties. The integration of CNT-based strategies with biology necessitates a multidisciplinary approach that requires competences in the diverse fields of chemistry, physics, and life sciences. In the biomedical domain CNTs are extensively explored as novel drug delivery systems for therapy and diagnosis. Additionally, CNTs can also be designed as new tools for modulation of molecular functions, by directly affecting various biological processes or by interaction with bioactive molecules. The aim of this review is to discuss how CNTs can be exploited as new probes for molecular functions. The different sections illustrate various applications of CNTs, including gene silencing, surface cell interactions via glycoproteins, biosensing, intracellular drug delivery using an atomic force microscopy tip-based nanoinjector, modulation of antibody/antigen interaction and enzyme activity, and blocking of ion channels. © 2010 Elsevier Ltd. All rights reserved.