Hepatocytes were cultured for 48 h in our standard culture medium (0.1 μM dexamethasone) or in the absence of dexamethasone. Then, the culture was continued under the same conditions, in the absence or presence of 10 μM rifampicin or 100 μM phenobarbital, and the cells were harvested 24 h later. The levels of the various CYP mRNAs in the presence (⁺dex) or absence (−dex) of dexamethasone were measured by RNase protection. The ratios of CYP mRNA (⁺dex)/CYP mRNA (−dex) are reported here. Data are from cultures FT159, FT160, and FT166.