Hyposensitization with a tyrosine adsorbed extract of Dermatophagoides pteronyssinus was effective in relieving symptoms in selected patients with perennial rhinitis due to this allergen who had responded poorly to topical application of steroids. There was a significant reduction in the nasal response to allergen after six weekly injections only in the actively treated group, but symptomatic improvement greater than that produced by placebo therapy was only evident after a further 10 months of monthly injections. Significantly more placebo-treated patients considered that therapy was ineffective and withdrew from the study. Only one patient developed significant unwanted effects from the injection therapy and had to be withdrawn from the study. We conclude that hyposensitization with a tyrosine adsorbed extract of Dermatophagoides pteronyssinus can be a safe and effective treatment for adults with perennial rhinitis due to this allergen who have responded poorly to nasal corticosteroids, and that those patients who eventually respond clinically are likely to have a diminished nasal response to allergen after the first 6 weeks of therapy.