Hops are told to promote sleep; manyfold efforts to detect the soporific principle have been unsuccessful so far. Preliminary pharmacological tests lead to the conclusion that the soporific activity of the exhalation of hops can be explained by its content of 2-methyl-3-butene-2-ol (1) in the volatile fraction. It was found that 1, when given to mice i.p. (0.80 g/kg) produces narcosis for about 8 h; no abnormal behaviour was observed there upon. Due to its water-solubility the concentration of 1 in the essential oil obtained by steam-distillation is low; contrary to that, 1, is enriched in the more volatile fraction of hops.