Twenty patients with recurrent nasal polyposis but without any history of aspirin sensitivity were given 2000 micrograms of intranasal lysine aspirin to one nostril and saline to the other once a week for periods of up to 15 months. Two patients had increased nasal obstruction following the initial test doses of lysine aspirin and were excluded from the trial proper. In the remainder symptomatic polyp recurrence was delayed compared with the previous experience while on intranasal steroids, with eight patients remaining symptom free at 15 months compared with an expected number of three (P = < 0.05, chi 2 test). Polyp recurrence was bilateral but there was a tendency for the lysine aspirin treated side to have less polyp tissue as assessed by nasendoscopy and by acoustic rhinometry.