During the last decade beta-adrenoceptor antagonists have become one of the first-line treatments for hypertension. Generally, they have been shown to be safe with a low frequency of serious side effects. However, minor subjective symptoms, usually considered to be CNS-related, have been reported for all beta-blockers used. Thus, all beta-blockers on the market seem to have a high benefit:risk ratio; independent of their physicochemical properties and pharmacodynamic profile, however, they seem to cause CNS-related side effects to about the same extent. These minor side effects, the mechanisms of which are unclear, consist of subtle effects on general well being, decreased initiative, a depressed frame of mind, and disturbed sleep. Generally, however, beta-blockers in therapeutic dosages do not affect the qualitative functions of the brain. The results so far available have been obtained primarily by using objective methods. Further comparison has now been initiated using documented subjective methods to investigate whether the objectively documented differences are of any clinical relevance to the patient's quality of life. Although it cannot be claimed with certainty, nonselective beta-blockers seem to cause CNS-related side effects to a greater extent than beta 1-selective blockers. Differences in the degree of hydrophilicity of the beta-blocker are apparently of no clinical relevance in this respect. Rather, the plasma concentration of the beta-blocking drug (degree of beta-blockade) seems to be the major determinant of whether or not CNS-related symptoms appear in susceptible patients.