The nasal cavity of 97 young healthy men (applicants for the pilot education in the Finnish Air Force) was examined. Bacterial culture demonstrated one or more species of aerobic bacteria in all 194 nasal cavities examined and anaerobic bacteria in 76.5%. In ten per cent of the cultures bacteria were detected after enrichment only. The most common aerobic bacteria were Staphylococcus epidermidis (79%), diphtheroids (41%) and Staphylococcus aureus (34%). Haemophilus influenzae was found in 5% and Streptococcus pneumoniae in 0.5%. Anaerobic culture yielded Propionibacterium acnes in 74.5% and Peptococcus magnus in 3.5%.