We have evaluated the efficacy of nedocromil sodium 2% eye drops in 35 patients (18 males and 17 females, mean age 32.8 yrs) suffering from perennial allergic conjunctivitis due to Dermatophagoides pteronyssinus diagnosed on the basis of anamnesis, Skin Prick Test and RAST. Patients were treated for 8 weeks with nedocromil sodium one drop each eye, four times daily and had to report the severity of the symptoms considered (photophobia, lacrimation, hyperaemia and itching) on a daily card. During the study no other medication was allowed. After 4 weeks symptoms were statistically improved and this beneficial effect increased at the end of the treatment. No side effects were reported. Nedocromil sodium eye drops is therefore a useful treatment in perennial allergic conjunctivitis due to Dermatophagoides pteronyssinus.