The glycosaminoglycan hyaluronan (HA, hyaluronate or hyaluronic acid) was quantified in rat lung during the development of bleomycin-induced lung injury. Extracted lung HA was measured by a radiometric assay. In control rats, the HA lung content was 95 +/- 5 (SE) micrograms/g of freeze-dried and homogenized lung tissue. After a single intratracheal instillation of bleomycin, the HA content of the lung increased significantly on day 1. Peak HA concentrations on days 3-7 averaged 70% higher than normal lung HA concentrations. From day 7 the HA concentrations progressively declined and had returned to normal by day 30. Qualitative assessment of lung HA has previously demonstrated that HA is accumulated in the edematous interstitial alveolar space during the alveolitis phase of bleomycin injury. Since high-molecular-weight HA has unique hydrophilic properties, another aim of the study was to elucidate the possible link between the increase in lung HA and the development of interstitial-alveolar edema postbleomycin. HA recovered by bronchoalveolar lavage from bleomycin-injured lungs increased with increasing total lung HA and had a mean molecular size of 220,000 +/- 50,000 (SE), indicating the minimum size of HA accumulated in the alveolar space. The relative lung water increased significantly on days 3-7 after bleomycin administration. A close relationship (P less than 0.001) and time dependence between the increase in relative lung water and the increase in lung HA were found.