The objective of this research was to determine if the homeopathic medicine Betula 30c is more effective than placebo at reducing symptoms of pollen allergy in patients sensitive to birch pollen. It was a double-blind, randomized, placebo-controlled trial. Tablets were given both as a prophylactic agent, once a week four weeks before the pollen season and as an acute remedy during the pollen season. The study was done in Oslo, Norway, in May 1996 and involved 73 children, adolescents and young adults from 7 to 25 y of age. Allergy-symptoms were assessed on a visual analogue scale (VAS) by patients or parents. Main outcome measure was the median (with its 95% confidence interval) of the symptom scores for all the treated patients, each day during a 10-day period. The pollen count was very low in 1996, only three days were high enough to provoke allergic symptoms. Surprisingly, the verum treated patients fared worse than the placebo group; they used more rescue medication and had higher symptom scores during these three days. Homeopaths might attribute the findings to a putative aggravation response, but the results certainly do not lend support to the usefulness of the tested prophylactic approach, under conditions of low allergen exposure.