Pulmonary fibrosis and inflammation induced in mice by biweekly injection of low doses (20 mg/kg) of bleomycin chronically administered subcutaneously was associated with a significant increase in T2 values measured in vitro (54.6 +/- 20.7 ms vs. 36.2 +/- 3.8 ms in controls). T1 values, however, were not altered significantly (613 +/- 124.6 ms vs. 666 +/- 105.7 ms in controls). Lung water content did not change (79.1 +/- 2.5% vs. 78.4 +/- 0.98% in controls, NS). Water content to dry weight ratio in the control group (3.63 +/- 0.212) did not differ significantly from that in the experimental group clinically treated with bleomycin (3.84 +/- .618). However, morphometric and histologic analysis indicated that in 71% of the chronically treated mice, there was marked pulmonary fibrosis (mean area of involvement 3.5 +/- 8.1% vs. 0.25 +/- 0.15% in controls, P less than .01). In addition, there was marked increase in pulmonary cellularity and infiltration by lymphocytes and macrophages (mean area of macrophage infiltration 8.71 +/- 13.256% vs. 1.17 +/- 1.404% in controls). The alteration in T2 in bleomycin damaged lung occurred in the absence of change in overall water content. However, the change in cellularity indicates an alteration of water distribution between the cellular, intravascular, and interstitial components induced by the measurable fibrotic and inflammatory response to bleomycin.