Although the dose of succinylcholine is customarily based on body weight this can be taken only as a rough guide. In the early phase after intravenous injection succinylcholine is partly removed by breakdown through the action of cholinesterase and in part by redistribution into the lean body mass. Sixty-six patients were given doses of succinylcholine based on lean body mass. 0.8 mg/Kg LBM was found to be quite adequate for complete muscle relaxation, permitting easy and atraumatic endotracheal intubation in all cases. Lean body mass was a better guide to dosage than body weight. Length of apnoea and duration of muscular paralysis were dose related; the bigger the dose the longer the response. However at 0.8 mg/Kg LBM they were better correlated with fat than with dose. Obese people have a relatively shorter recovery time from apnoea and muscular paralysis.