The mRNA levels for several GABAA receptor subunits were measured by Northern blot analysis. Rats were treated for 3 wk by continuous release of diazepam (DZP) from subcutaneous reservoirs, and then sacrificed immediately or 48 h after removing the reservoirs. Poly(A)+ RNAs, isolated from cerebral cortex, cerebellum, and hippocampus, were hybridized with oligonucleotide probes for GABAA receptor subunits and a cDNA probe for beta-actin. Subunit mRNAs were expressed relative to the corresponding beta-actin mRNA. DZP treatment decreased the alpha 1 subunit mRNA level 40% in hippocampus, but it was not changed in cortex or cerebellum. The alpha 5 subunit mRNA level was decreased in cerebral cortex (28%) and hippocampus (15%). The gamma 2 subunit mRNA level was decreased (40%) only in cortex. DZP treatment did not affect alpha 2, alpha 3, alpha 4, beta 2, or beta 3 subunit mRNA levels. Decreases in mRNA levels had reversed within 48 h after stopping chronic treatment. Acute DZP did not change alpha 1, alpha 5, or gamma 2 subunit mRNA levels. The decreases in GABAA receptor subunit mRNA levels were specific to subunit and brain region. These results, coupled with those after chronic flurazepam treatment, also indicated that the effects on GABAA receptor subunit mRNA levels are specific to the benzodiazepine (BZ) used for chronic treatment.