The pyrokinin/pheromone biosynthesis activating neuropeptide (PBAN) family of peptides in insects has been shown to have diverse physiological functions, including stimulation of pheromone biosynthesis, muscle contraction, melanization and acceleration of puparium formation. An active core of a 5-amino-acid C terminal sequence, FXPRLamide, required for physiological functions, characterizes this family of peptides. Immunocytochemical techniques were used to demonstrate the presence of pyrokinin/PBAN-like peptides in the central nervous system of adult and larval mosquitoes, Culicidae. The ventral nerve cord of Culicidae consists of the subesophageal ganglia (SEG), three thoracic ganglia and six or eight abdominal ganglia in larvae and adults respectively. Immunoassays with an anti-PBAN antibody and FITC labeled detection probe revealed three groups of peptide-producing cell bodies in the SEG. The peptide was also observed in axons originating in the SEG and terminating in the terminal abdominal ganglion (TAG). A pair of reactive cell bodies was detected in the first thoracic ganglion and all abdominal ganglia with the exception of the TAG. A neurohemal organ containing reactive peptide was associated with the pair of cell bodies in each abdominal ganglion. These results show that the mosquito nervous system contains pyrokinin/PBAN-like peptides and that these peptides likely are released into the hemolymph.