BACKGROUND : Diagnostic procedures using natural extracts show only limited quantitative correlation between in vivo and in vitro results. Highly pure recombinant allergens might show more predictive findings. OBJECTIVE : The aim of this study was to compare natural birch pollen extract (BPE) and recombinant Betula verrucosa (rBet v 1) for their diagnostic value comparing skin prick tests (SPTS) and nasal provocation tests (NPTS) with specific IgE in the serum. METHODS : Thirty-four patients allergic to birch pollen and five healthy controls were investigated. SPT and NPT were performed with BPE and rBet v 1 at different concentrations. Specific serum IgE was measured by the Pharmacia CAP system. RESULTS : Commercial BPE and rBet v 1 (10 micro g/mL) were able to elicit similar allergenic reactions in vivo and IgE binding in vitro. SPT reflects immediate-type allergy as determined by NPT to a higher degree than specific IgE, for both reagents. To cause allergic reactions in NPT, higher amounts of rBet v 1 were needed than for skin tests and the sensitivity was lower than with BPE. CONCLUSION : rBet v 1 alone is sufficient for a reliable diagnosis of birch pollen allergy in most patients and induces comparable skin test reactivity as BPE, but less allergic reactions in nasal provocations.