The distributions of asthma, hay fever and eczema were examined in the first degree relatives of 516 asthmatics grouped according to atopic status, history of hay fever/eczema and history of asthma provoked by pollens, dust or animals. The prevalences of both asthma and eczema in relatives were strongly correlated with the presence of hay fever/eczema in probands and to a lesser extent with their atopic status. The prevalence of hay fever in relatives was strongly correlated with both the presence of hay fever/eczema and the degree of atopy in probands. In contrast, allergic provocation of asthma in probands did not influence the prevalences of asthma, hay fever or eczema. These findings are consistent with the hypothesis that there is an increased risk of asthma in relatives of atopic asthmatics which may arise from the enhanced susceptibility to asthma of individuals who inherit both a predisposition to asthma and a predisposition to atopy.