An application of receptor models to the analysis of data on beta-adrenoceptor blockade.

1. The classical single receptor competitive occupancy model accurately describes the joint action of an agonist (isoprenaline) and a beta-adrenoceptor antagonist (propranolol) or some partial agonists (dichlorisoprenaline, practolol) on the positive chronotropic response in rats which have been depleted of catacholamines. 2. The mathematical form of the model suggests that the dissociation constants of classical competitive partial agonists may be assessed using dose ratios by exactly the same method as that currently used for agonist-antagonist interactions, provided that the log dose-response curves are first suitably normalized. 3. Close agreement between the theoretical mathematical models and the experimental data can be demonstrated by statistical fitting for certain beta-adrenoceptor antagonists (propranolol, dichlorisoprenaline, practolol). 4. The model fails to describe the behaviour of other beta-adrenoceptor antagonists (oxprenolol, pindolol). A possible extension of the model to include these drugs is proposed.