The penetration ofCladosporiumspores and spore aggregates into human airways was studied using three different spore sampling methods: 1) a Burkard spore trap for determining the aggregation degree ofCladosporium; two samplers, simulating the human respiratory system, 2) a 6‐stage Andersen 2000 sampler, and 3) a new size‐selective bioaerosol sampler (SSBAS), designed specifically for immunochemical and chemical analyses. The aggregation degree ofCladosporiumspores varied between 1.0 and 1.3 spores per dispersal unit. Grouping seems to be of little if any importance to the penetration ability ofCladosporiumspores into the respiratory tract. The distribution of spores in the Andersen and SSBAS differed significantly in the largest size class (spores2.1 μm in diameter are trapped. In the SSBAS altogether 99.4% of spores were found in the first two filter stages (cutoff point approx. 2.5 μm in diameter). Conclusions regarding the penetration of spores to the lungs on the basis of aerobiological results should always be based on the use of properly calibrated spo