The technique of intracerebroventricular (i.c.v.) injection is a useful neuroethological tool for studying the central actions of drugs on behavior of conscious animals because many drugs do not cross the blood–brain barrier, which limits the extent of drug action to the CNS. In this chapter we propose a rapid, safe, and inexpensive method for i.c.v. injection in adult zebrafish which does not require implantation of a guide cannula.