Obesity is associated with significant changes in body composition and function that may alter the pharmacodynamics and pharmacokinetics of various drugs. In this study, we investigated the neuromuscular effects of cisatracurium in morbidly obese as compared to control group of normal body weight patients. In the morbidly obese group (n = 20), corrected weight was used to calculate the drug doses. In the control group (n = 20), the dose was calculated on ideal body weight (IBW). 0.15 mg/kg(-1) cisatracurium was administered as the neuromuscular blocker. Neuromuscular effects were recorded at T0 (onset time), T1 (appearance of first stimulus of TOF), T25 (25% recovery of T1) and T25-75 (time of T25 to T75, recovery time). T0 was determined as 177 +/- 23 s and 168 +/- 19 s in the morbidly obese, and control group, respectively. T25 was determined as 46 +/- 7 min and 56 +/- 8 min, in the morbidly obese and control group, respectively (p < 0.05). T25-75 was determined as 11 +/- 5 min and 14 +/- 6 min in the morbidly obese and control group, respectively (p < 0.05). Intubation conditions were determined as good in 13, excellent in 7 patients in the morbidly obese group, and as good in 4 and excellent in 16 patients in the control group (p < 0.05). As different neuromuscular effects of cisatracurium were detected, we conclude that ne uromuscular agents must be monitored in the morbidly obese patients.