This was a multicentre, double-blind, randomized group comparative study in which 77 children, aged 6–16 years, received 2% nedocromil sodium eye drops and 72 received placebo, one drop into each eye twice daily. The treatment period was 4 weeks, covering the peak birch pollen season. Prior to the start or the season, patients who had mended the clinic the previous 2 years because of seasonal allergic conjunctivitis (SAC) to birch pollen, entered a one week baseline period during which symptoms were assessed, diary cards completed, and routine sampling of blood and urine earned out. The double-blind treatment period then commenced at the onset of the birch pollen season. Patients parents kept daily diary record cards of eye symptom severity and concomitant therapy. Conjunctivitis was mild in both treatment groups but nedocromil sodium was more effective than placebo in controlling symptoms. During the 2–3 weeks of peak pollen counts, this therapeutic effect was statistically significant for itching (P <0–01), watering (P <0.05) and total symptom score (P <0.01), but was not significant for grittiness (P= 0.08) or redness (P = 0.06). Global opinions of efficacy showed no difference between treatments, due to a high placebo effect (however, the diary card data indicated a significant improvement with nedocromil sodium). We therefore conclude that nedocromil sodium 2% eye drops, administered twice daily, is an effective treatment for SAC in children.