OBJECTIVE: To investigate whether exposure to cigarette smoke causes histopathological changes in tissues of the heart, liver, kidney, testis, spleen, brain, and lung just after exposure, and whether smoke and smoking termination affect malondialdehyde (MDA) levels and catalase activities. STUDY DESIGN: Forty rats were divided into 5 groups: control, rats exposed to cigarette smoke, and rats previously exposed to smoke that stopped smoking for 1 month, for 3 months, and for 5 months. Tissue samples from all groups were collected to measure MDA and catalase activities. RESULTS: MDA levels in heart tissue of rats exposed to smoke were relatively higher than those of the control group. Rats that stopped smoking for 1 and 3 months also had significantly higher MDA levels. Catalase activity in liver and kidney tissues of rats exposed to smoke was significantly lower than that of the control group. Histopathologic changes were observed only in the lung. There was a statistically significant difference only between the lungs of the smoking group and all other groups. CONCLUSION: Cigarette smoke exposure results in reduced catalase activity in liver and kidney tissues, elevated catalase activity in spleen tissue, and increased MDA levels in heart tissue. The lung is the primary target organ affected by smoking. © Science Printers and Publishers, Inc.