Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of mRNA expression for MDR-related gene products on lung cancer cell lines grown as monolayers or MTS. The expression of the following genes was evaluated: MDR-1, MRP-1, Topo IIα, Topo IIβ, GST-μ, Topo I, and G3PDH. Amplification products were electrophoretically separated in polyacrylamide gels and revealed by etidium bromure staining. The analysis of G3PDH expression was used as constitutive control for the integrity of RNA molecules. A) Representative RT-PCR and B) Densitometric analysis of RT-PCR band intensities for MDR-related genes normalized by G3PDH. Data are mean ± standard deviation (SD) of three independent experiments.