Pharmacological evidence suggests that GABA may play an important role in regulating the secretory and synthetic activity of the hypothalamic periventricular somatostatin (SOM) neurones controlling growth hormone secretion. In this study, we have utilized a dual labelling in situ hybridization technique to examine whether the alpha 2 sub-unit of the GABAA receptor, which is abundant in this region, is expressed by periventricular SOM neurones. Neurones expressing SOM were detected using an alkaline phosphatase-labelled antisense oligonucleotide and the alpha 2 sub-unit with an 35S-labelled antisense oligonucleotide. Hybridization experiments with the alpha 2 sub-unit probe alone confirmed the high level of mRNA expression for this sub-unit in the rat periventricular region and simultaneous hybridization experiments with both probes revealed that > 90% (93 +/- 2%) of periventricular SOM neurones express the alpha 2 sub-unit of the GABAA receptor. These results provide the first direct evidence that periventricular SOM cells possess GABAA receptors and suggest that the great majority of these neurones synthesize a GABAA receptor containing the alpha 2 sub-unit.