Antisera against the pigment-dispersing factor (PDF) and corazonin (Crz) reacted with distinct sets of neurons in the cephalic ganglia of termites. The locations of immunoreactive cells were similar but their numbers differed among the eight species examined: PDF-ir occurred in 0-6 cells in each optic lobe and 1-2 pairs of cells in the subosophageal ganglion (SOG), and Crz-ir in 0-2 pairs of cells in the pars intecerebralis, 3-14 cells in each lateral protocerebrum, and 0-6 pairs of cells in the SOG. Staining patterns were identical in the pseudergates, soldiers, and substitutive reproductives of Prorhinotermes simplex. Workers and soldiers were compared in the remaining 7 species. The only caste divergence was detected in Coptotermes formosanus, in which the soldiers differed from the workers by lack of 4 Crz-ir perikarya in the pars intercerebralis and occasionally also by the absence of 2 Crz-ir perikarya in the SOG. Diurnal changes in PDF-ir and Crz-ir were examined in P. simplex kept under long day (18:6h light:darkness) or short day (10:14 h) photoperiods. No circadian fluctuations in the distribution or the intensity of immunostaining were found in the pseudergates and soldiers that were sacrificed in 4h intervals or in the male and female substitutive reproductives examined in 6h intervals.