The effect of salbutamol (a comparatively selective adrenergic β2- receptor agonist) on the peripheral platelet concentration was studied before and after the ingestion of either 50 mg metoprolol or 40 mg propranolol. The study was carried out on healthy male volunteers and autologous slCr-labelled platelets were employed at the experiments. Salbutamol was infused intravenously over a period of 6 min in a dose of 0.27 μg kg-1 min-1. Prior to metoprolol and propranolol administration a statistically significant lowering in platelet-bound radioactivity (PBR) was obtained in response to the salbutamol infusions. This salbutamol-induced fall in PBR was completely blocked by propranolol but was left unaffected by metoprolol. It is concluded that adrenergic β2-receptor stimulation induces a transient lowering of the peripheral platelet count.