The GABAA receptor subunits are candidate genes for panic disorder because the receptor is the site of action for the anxiolytic effects of the benzodiazepines. We tested for linkage between a tetranucleotide repeat polymorphism at the GABAA beta 1 locus, located on chromosome 4p13-p12, and panic disorder defined by DSM-III-R criteria in 5 Icelandic pedigrees. Both a narrow affection status (definite panic disorder and agoraphobia) and a broad one (including probable cases of these disorders) were tested. With the narrow definition, at a recombination fraction of 0.00, the lod scores in the 5 pedigrees ranged from -3.240 to +0.063, the total score across all 5 pedigrees being -8.299. With the broad definition at the same recombination fraction, the individual lod scores ranged from -2.614 to -0.489, with the total being -8.089. Thus, linkage between panic disorder/agoraphobia and the GABAA beta 1 locus in these pedigrees is exceedingly unlikely.