Abstract/Text: The hyperventilation syndrome (HVS) can be regarded as a form of panic disorder associated with a relative increase in sympathomimetic tone, the effects of which can be counterbalanced by beta-adrenoceptor blockade. The efficacy of the beta-blocker bisoprolol was investigated in a double-blind placebo-controlled randomised crossover trial involving 60 patients from 17 general practices. Following a single-blind placebo prephase, patients who met the inclusion criteria were randomised to treatment with either 5 mg bisoprolol or an identical-looking placebo tablet once daily for three weeks. They were then crossed over to the other treatment arm. At the end of each treatment phase the number of hyperventilation attacks and the severity of symptoms were assessed and side effects recorded. The number of attacks decreased from 4.04 per week at baseline to 3.52 with placebo and to 1.26 with bisoprolol. The decrease of attacks with bisoprolol was significant (p < 0.05) compared to baseline and placebo. The severity of the complaints improved from 29 (scale 0 to 64) at baseline not significantly to 26 with placebo and significantly (p < 0.05) to 15 with bisoprolol. No serious side effects were reported. Five milligrams of bisoprolol once daily is effective and safe in the maintenance of symptom reduction in patients with the hyperventilation syndrome.