A study of the consistency of responses by allergic patients in repeated studies of the homeopathic remedy Betula 30c or placebo against birch pollen allergy, was made. A randomized, double-blind, placebo-controlled trial was performed including participants with a known allergy to birch pollen. Allergy symptoms were assessed on a visual analogue scale (VAS) by patients or parents each day during a 20-day period during two different pollen seasons. The work was carried out in Oslo, Norway during May 1995, 1996 and 1997. There were 51 patients ranging in age from 7 to 50y. The homeopathic remedy Betula 30c or placebo was given as tablets, both as a prophylactic agent, once a week for 4 weeks before the pollen season started, and as an acute remedy during the pollen season. The mean value of the symptom scores on the visual analogue scale, for all registration days from each patient was the main outcome. The patient groups that received either placebo or Betula 30c for two successive years showed a consistent response (r=0.75, P=0.01 and r=0.70, P=0.003, respectively). No such correlation was found in the two groups that changed remedy from one year to another (either from placebo to Betula or vice versa). Subjective assessment of allergic symptoms to birch pollen differed more from one year to another when different regimens (placebo or homeopathic) had been administered these two seasons, than when the same treatment had been given.