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Patients with chronic, unexplained cough were investigated for the diagnosis of occult asthma by methacholine bronchoprovocation test. Sixteen out of 26 cases showed hyper-reactivity of the airways with 20% or more reduction in FEV1 after a Provocation dose of 2.5 mg/ml or less. None of the 16 control subjects reacted with this dose. It is concluded that asthma is an important cause of chronic cough in this region and in case of suspicion methacholine bronchoprovocation test is helpful.