This study examines the relations of allergy skin-test reactivity, assessed by prick testing, to a variety of respiratory symptoms, findings, and diagnoses in a general population sample consisting of more than 3000 subjects. The independent and combined relations of skin-test reactivity and cigarette smoking are reported. Prevalences of asthma and allergic rhinitis are closely related to the severity of skin-test reactions; all of the 39 subjects with the largest skin-test reactions observed have had one or both of these conditions. A variety of other respiratory findings, not generally considered allergic in nature, are also related to skin-test reactivity, especially in children and in young to middle-aged adults. In subjects 15 to 54 years of age, an atopic predisposition, as manifested by reactions to allergy skin tests, appears to be associated with an increased susceptibility to the bronchoconstrictor effects of cigarette smoking and to recurrent chest infections. It is suggested that an atopic predisposition relatively early in life may be a risk factor for the later development of chronic obstructive lung diseases.