Sensitization to mould spores was investigated in six patients with hypersensitivity pneumonitis, eight patients with idiopathic lung fibrosis, and six healthy controls by immunodiffusion and immunofluorescent testing of personal spore samples. The new technique of personal spore sampling with the Burkard personal volumetric air sampler and indirect immunofluorescent test for detection of spore-specific IgG and IgM confirmed that five patients with hypersensitivity pneumonitis and four with lung fibrosis were actually exposed and sensitized to moulds. Personal spore sampling and subsequent immunofluorescent tests represent sensitive tools for detection of individual mould sensitization and air quality control.