Repeated conjunctiva] provocation tests ICPT) were done in 20 children with rhino-conjunctivitis due to birch pollen allergy. Compared with the first open challenge, three successive blinded CPTs were reproducible within an allergen strength difference of one 10-potency in 92 of the tests. Based on the data, a power function was constructed, making it possible to determine the number of patients needed to discriminate CRT sensitivity of a given magnitude between two populations. During the study period specific serum-IgE increased in only three of 19 patients, indicating that stimulation of IgE antibody production is not a common consequence of repeated tests. We conclude that CPT is useful in clinical research. When indicated in clinical routine. CPT is a sale and easy test with good precision.