Background: The aim of this study was to evaluate paraoxonase-1 (PON1) and arylesterase (ARE) activities and oxidative stress status in patients with colorectal carcinomas (CRC). Materials and methods: Thirty-three patients (20 male, 13 female) with CRC and 30 healthy controls were enrolled in the study. Blood samples were obtained from the CRC patients before adjuvant therapy. Serum samples from CRC patients and healthy controls were analyzed for PON1 and ARE activities. Results: The PON1 and ARE activities of the patients with CRC were significantly higher compared to those of the control group (PON1 activity is 125.35 +/- 20.07 U/L for CRC patients and 1.22 +/- 0.48 U/L for control group, P<0.001; ARE activity is 160.76 +/- 10.79 U/L for CRC patients). ARE levels showed a positive correlation with smoking status (P=0.04). PON1 activity was higher in colon carcinoma patients (135.95 +/- 19.3 U/L) rather than rectal carcinoma patients (97.08 +/- 5.24 U/L) but it was not statistically significant (P=0.72). Conclusion: Serum PON1 activity is increased in patients with CRC, and serum ARE levels showed a positive correlation with smoking status. PON1 activity was higher in colon carcinoma patients. There is no other study in literature investigating these activities for CRC patients. It should be reevaluated by larger clinical trials.