Cigarette smoke (CS) exposure regulates retinoic acid (RA) signaling components in the lung. C57BL/6 mice were exposed to room air/no smoking (NS) or CS for 1 month (1M), 3 months (3M), or 6 months (6M). The mRNA expression of the RA signaling components in the lung was measured using quantitative polymerase chain reaction (PCR). The relative mRNA levels of RA receptor (RAR) α (A), RARβ (B), RARγ (C), retinaldehyde dehydrogenase (RALDH) 1 (G), RALDH2 (H), and cytochrome P450 family 26 subfamily B polypeptide 1 (Cyp26b1) (I) are shown (n = 5 mice/group). The protein levels of RARα (D), RARβ (E), and RARγ (F) in the lung of mice exposed to NS or CS for 6 months were assessed using Western blotting. Data are representative of three experiments. *P < 0.05.