Besides their effects on air hygiene and health, bioaerosol particles play an important role in cloud physics, for example, some bacteria are able to accumulate water and act as ice nuclei. For sampling aerosol particle impactors were used. The larger particles were sampled size fractionated with a free wing impactor while for the smaller ones an isokinetic two-stage impactor was constructed. The bioaerosol particles of the coarse fraction were stained with a protein dye and could be distinguished from the non-dyed particles using an optical light microscope. The small particles were examined in a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX). Three criteria were used to characterize the particles: morphology, elemental composition and behaviour during EDX. Literature and the results of our own experiments with test aerosols showed that biological particles have a special morphology together with a special elemental composition and also some of them change their form during EDX. Based on these criteria a scheme was developed dividing the atmospheric aerosol into six groups, each of them representing biological or non-biological particles.