BACKGROUND: As the population of immunocompromised patients continues to grow, the incidence of infections caused by opportunistic filamentous fungi will continue to increase. Inhalation of fungal spores which are found in the environmental air precedes infection with molds. We investigated the relative frequency of various molds recovered from hospital air as compared to isolates from clinical specimens. METHODS: Air samples were taken from 83 sites in Chonnam University Hospital during December 1997. Air sampler (Biotest, Germany) with Rose Bengal agar strip (Biotest, Germany) was calibrated to take 40 liters of air. The strips were incubated at 37degrees C for 2-14 days. The results of air cultures were compared with those from the clinical specimens during a year (1997). RESULTS: Of 83 air samples cultured, 61 (73.5%) were positive for molds: 43 (51.8%) samples with 1-2 CFU, 15 (18.1 %) samples with 3-5 CFU, and 3 (3.6%) samples with > 5 CFU. A total of 184 molds were isolated and the most frequently recovered molds were Cladosporium (26.0%), followed by Penicillium (25.5%), Aspergillus (18.5%) and Alternaria (9.8%). The most frequently isolated molds from clinical specimens were Aspergillus (62.8%) and Fusarium (20.2%). For Aspergillus species, A. flavus (28,8%) and A. fumigates (25.4%) were predominant among the clinical isolates, whereas A sydowii (44.1%) and A. niger (38.2%) were common in the hospital air. CONCLUSION: This result shows that Cladosporium and Penicillium are the predominant molds in the hospital air and the relative frequency of molds recovered from hospital air is quite different from those of clinical isolates.