The duration of action and recovery of 0.6 mg kg-1 rocuronium in underweight, normal weight, overweight and obese patients were investigated. Forty-eight patients were divided into four groups, according to their body mass index, and were given 0.6 mg kg-1 rocuronium. The onset time, the duration 25% and either the spontaneous or induced recovery were measured according to the random assignment. The onset time in the obese group was shorter 60 (50-90) s compared to the other groups (underweight: 95 (40-320) s, normal: 95 (50-200) s, overweight: 90 (50-260) s, but the difference did not reach the level of statistical significance. The duration 25% was slightly prolonged in the obese patients (31.5 (21.0-61.0) min) when compared to the underweight (25.0 (15.0-37.0) min), normal weight (26.0 (20.0-36.0) min) and overweight (27.0 (19.0-35.0) min) patients. No differences were observed in spontaneous (9.5-12.5 min) and induced (2.5-3.5 min) recovery.