The final point to be made is that RNA studies are only the first step in localizing the distribution of adrenergic receptors in human tissues. Although RNA levels tend to correlate well with receptor protein expression in many tissues, this must be confirmed with studies aimed at receptor protein. Selective antibodies are being developed currently by various researchers and selective ligands by several pharmaceutical companies. In the next few years, not only should it be possible to confirm or modify results of adrenergic receptor subtype distribution studies, it also should be possible to design and test specific hypotheses related to adrenergic receptor diseases in whole animal models with newly developed subtype-selective ligands. Because species heterogeneity in adrenergic receptor tissue distribution exists, final testing of adrenergic receptor subtype-selective drugs will have to occur in humans. This is a potentially exciting possibility for anesthesiologists, for what better clinical laboratory is there than the operating room? Hence, anesthesiologists are in a key position to help redefine human adrenergic physiology once new adrenergic receptor subtype-selective agents become available.