A study was made of airborne bacteria and fungi in a cellulose facility, and antibody levels were measured in ten employees with work related symptoms suggesting microbial allergy. Subjects included six caterpillar drivers on outdoor wood chip piles and four workers in the barking department, aged 37 to 56 years. Each worker had one or more symptoms including rhinitis, eye irritation, cough, fever, muscle pain and dyspnea. A six stage Andersen impactor was used to obtain air samples for analysis of thermotolerant fungi and mesophilic fungi and bacteria in terms of colony forming units per cubic meter of air (cfu/m3). Antigens were prepared from these cultures for use in enzyme linked immunosorbent assays of specific antibodies in employees' sera. Barking workers were exposed to bacteria more than fungal spores (respective geometric mean concentrations of 46.3x10(3) and 5.9x10(3)cfu/m3). Wood chip pile workers were exposed to fungal spores more than bacteria (respective concentrations of 1.5x10(3) and 45.5x10(3)cfu/m3). Predominant fungal species were Rhodotorula-glutinis in the barking department and Aspergillus-fumigatus and Penicillium-brevicompactum on wood chip piles. Highest levels of specific immunoglobulin-G were against Paecilomyces-variotii, Sporobolomyces-salmonicolor and Aspergillus- niger. Lowest levels were against Rhizopus-nigricans, Humicola- grisea and Streptomyces-albus. There were no differences in levels of bacterial antibodies between worker groups, while fungal antibodies were detected in levels two to five times higher in wood chip pile workers. The authors conclude that the physical nature of aerosols as well as microbial concentrations should be considered for health risk evaluations of airborne microbes.