In the present study, we investigated the key molecules that determine gamma-aminobutyric acid (GABA)ergic signal transduction in the parabrachial/Kölliker-Fuse complex (PB/KF) by means of immunocytochemistry and in situ hybridization. Our data demonstrate a dense plexus of GABA-immunoreactive (-ir) varicosities throughout the nuclei of the PB and the KF. The number of neurons expressing GAD65 or GAD67 mRNA was fairly low in the PB, whereas caudally in the KF an accumulation of GAD-expressing neurons was observed. The GABA transporter-3 (GAT-3) was detected in all parts of the PB/KF, whereas immunolabeling for GAT1 was not observed. All nuclei of the PB and the KF exhibited immunoreactivity for the gamma2-, alpha2-, and alpha3-subunits of the GABA(A) receptor. Gamma2-ir was strong and similar in all PB/KF nuclei. In contrast, alpha2-labeling was particularly intense in the superior lateral PB, and alpha3-labeling was most prominent in the external lateral and external medial PB, compared with the remaining nuclei. With respect to the subcellular localization, we found gamma2-ir in cell bodies and higher order dendrites, whereas alpha2- and alpha3-ir was predominantly found in cell bodies. Immunolabeling for the beta2/3- and the alpha1-subunit was seen in cell bodies and presumed dendritic profiles. The staining intensity was strongest in the dorsal lateral PB. Most importantly, the external lateral PB and the waist area were totally devoid of beta2/3- and alpha1-ir. Our data suggest that neural processing in the PB/KF is under a strong GABAergic inhibition that is apparently mediated by different types of GABA(A) receptors in functionally different pathways through the PB/KF.