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The principal objective was to evaluate the functional and structural integrity of precision-cut rat lung slices in culture over 72 h.Lung slices metabolized 7-ethoxycoumarin in a time-dependent fashion, the major metabolites being the sulphate and glucuronide of 7-hydroxycoumarin with very low levels of the free compound. Prior treatment of rats with β-naphthoflavone elevated markedly the rate of metabolism. The optimum slice thickness, as exemplified by the metabolism of 7-ethoxycoumarin, was about 600 μm.Lung slices retained metabolic viability towards 7-ethoxycoumarin for 8 h, but after this point a marked decline in metabolic activity was noted. However, very low levels of activity were still evident following a 72 h incubation.Morphological examination of lung slices revealed nuclear degeneration and loss of tissue architecture following 24 h incubation. When cellular integrity was assessed using lactate dehydrogenase, a time-dependent leakage was evident with maximum loss occurring within 24 h; longer incubations did not result in further leakage.It is concluded that precision-cut rat lung slices, of 600 μm thickness, can be maintained metabolically viable in culture for some 8 h.