There is a growing body of research on using carbon nanotubes (CNTs) and other nanomaterials in neural engineering. Scientists are already exploring the feasibility of using CNTs to probe neural activity. With this research comes the need to develop a unified approach when assessing the toxicity of CNT in neurons. However, a complex picture emerges from the reported data: is it feasible to develop CNT-based devices as drug delivery vectors? Ultimately, are soluble CNT neurotoxic, and, if yes, to what degree? Given the often conflicting results of research reports on the biocompatibility of soluble CNT when administered to neurons in the central nervous system, a review article helps to clarify which aspects (technical or methodological) of these studies may be responsible for their heterogeneous conclusions.