The aim of the study was to determine the seasonal variability of the airborne microflora in a hospital ward of the pneumonological department, with regard to potential impact on respiratory status of asthmatic patients hospitalized in the ward. Microbiological air sampling was carried out for a period of 1 year from June–May, during work-days, 16-21 days per month. Each day, the air samples were collected twice: in the morning at 09:00 and in the afternoon at 13:00. Air samples were taken with a custom-designed particle-sizing slit sampler enabling estimations of both total and respirable fractions of the microbial aerosol. Air samples for determination of bacteria were taken on blood agar and air samples for determination of fungi were taken on Sabouraud agar. Mean monthly concentrations of total microorganisms (bacteria + fungi) in the air of the examined hospital ward were between 296.1–529.9 cfu/m³. Mean monthly concentrations of airborne bacteria ranged from 57.1–436.3 cfu/m³, with peak values in November and May and the lowest values from December to February. Mean monthly concentrations of airborne fungi showed much greater variation than bacteria and ranged from 9.9–96.1 cfu/m³ with the very distinct peak in November and the lowest value in May. The variations in monthly concentrations of total microorganisms, bacteria and fungi in the air of hospital ward were statistically significant (p<0.001). The concentrations of total airborne microorganisms, bacteria and fungi recorded in the hospital in the morning were significantly greater compared to those recorded in the afternoon (p<0.01). The mean monthly values of respirable fraction for total microorganisms were within a range of 17.3-44.4%, for bacteria within a range of 17.2-44.8%, and for fungi within a range of 2.2-39.1%. The most common microorganisms in the air of the examined ward were Gram-positive cocci which accounted for 31.4-46.4% of the total count. Gram-negative bacteria and corynebacteria were less numerous, forming respectively 11.8-27.5% and 9.6-20.0% of the total count. Endospore-forming bacilli and actinomycetes occurred in small proportions, respectively 0.3-3.2% and 0-2.0% of the total count. Fungi formed 7.6-42.5% of the total count. The prevailing species was Aspergillus fumigatus which constituted on average 77.0% of total fungal strains isolated from the air of the hospital ward. A significant decrease of spirographic indices (VC, FEV 1) in asthmatic patients hospitalized in the ward, at increase of the concentration of airborne bacteria and/or fungi, was found in 9 out of 24 examined patients (37.5%) and in 19 out of 192 analysed single relationships (9.9%). In conclusion, although acteria and fungi occurred in the air of the examined hospital ward in relatively low numbers (of the order 10²cfu m³ and 10¹cfu/m³ respectively), they should be considered as a possible cause of asthma exacerbations in some patients because of the presence of Aspergillus fumigatus and other potentially pathogenic species.