Clinical use of bone marrow mesenchymal stem cells (BMMSCs) holds great promise for regenerative medicine in intractable lung diseases, such as lung fibrosis or acute respiratory distress syndrome. However, a severe obstacle to the clinical application of BMMSC transplantation is the time-consuming, laborious processes required for cell culture. In order to evaluate the clinical applicability of BMMSC transplantation, we tested whether engraftment of minimally cultured BMMSCs ameliorates progressive fibrotic lung injury.Differences between murine BMMSCs cultured for 2 h (2-h adherent BMMSCs) and conventionally (9-day) cultured BMMSCs were examined in vitro. The effects of grafting either type of BMMSCs on fibrotic lung injury were then assessed by transfer experiments in a murine bleomycin-induced lung fibrosis model, in which donor cells were administered 3 days after challenge.2-h adherent BMMSCs were smaller, less granular, possessed higher proliferative capacity and expressed higher levels of several stem cell markers and chemokine receptors than 9-day cultured BMMSCs, but lower type I procollagen, a-smooth muscle actin, tumour necrosis factor-b and oncogenic transcription factor c-Myc, suggesting that they may be advantageous for cellbased therapy compared with 9-day cultured BMMSCs. Grafting 2-h adherent BMMSCs ameliorated inflammatory and fibrotic lung disorders, and reduced mortality equally well or better than 9-day cultured BMMSCs.Minimally cultured BMMSCs can substitute for conventionally cultured BMMSCs and will be a promising cell source for the treatment of acute fibrotic lung injury.