Table 1.

Study design.

	Visit 1 Inclusion	Visit 2 Baseline out of season	Visit 3 Birch pollen season
Blood sample	x	x	x
Spirometry	x	x	x
Skin prick test	x
Specific IgE for birch	x
Nasal lavage		x	x
Induced sputum		x	x
Diary
- symptoms			x
- medication			x
- PEFR			x

x: performed investigations at each visit