Objective: To evaluate whether thermal energy produced by laser and bipolar electrosurgery during laparoscopic procedures significantly elevates blood carboxyhemoglobin levels. Methods: We prospectively studied 27 healthy nonsmoking patients, mean ± standard deviation (SD) age 39.1 ± 8.0 years (range 22-56), scheduled for laparoscopic procedures in which smoke was generated. Prolonged operative laparoscopy involved high-Blow carbon dioxide insufflation, intensive evacuation of intra-abdominal smoke, and controlled hyperventilation with 50-100% oxygen. Laser and bipolar electrosurgery were used in all cases. Blood samples were drawn before and after surgery. Carboxyhemoglobin concentrations were measured using a highly accurate gas chromatography method. Results: The mean ± SD duration of surgery was 141 ± 72 minutes (range 45-300). The mean ± SD carboxyhemoglobin levels were 0.70 ± 0.15% (range 0.44-1.20%) before surgery and 0.58 ± 0.20% (range 0.30- 1.33%) after surgery. A significant decrease (P < .001) in carboxyhemoglobin concentrations occurred during surgery (mean ± SD, 20 ± 11%; range 3-46%). The carboxyhemoglobin level was increased at the end of surgery in only one woman. In only one patient did the levels exceed 1% (1.33%), still well below the human threshold tolerance level of 2%. The Spearman correlation coefficient between carboxyhemoglobin concentrations and duration of surgery was r = 0.308 (P = .12). Conclusion: Carbon monoxide (CO) poisoning is not associated with even prolonged laparoscopic surgical procedures. This may be attributed to aggressive smoke evacuation that minimizes exposure to CO, and to active elimination of CO by ventilation with high oxygen concentrations.