OBJECTIVE To investigate the doses of antivenom administered to adult patients with severe brown snake envenoming. DESIGN AND SETTING Review of charts from Western Australian adult teaching hospitals, December 1991 to December 2001. PATIENTS 35 patients with severe brown snake envenoming, defined prospectively as afibrinogenaemia (< 0.3 g/L) after a bite by a brown snake (genus Pseudonaja). MAIN OUTCOME MEASURE The dose of antivenom required to neutralise venom, defined prospectively as the dose of antivenom given before the return of detectable fibrinogen levels. RESULTS Of 88 patients with brown snake envenoming admitted over the 10 years, at least 35 had severe envenoming. Afibrinogenaemia persisted for 10 hours (range, 1.4-68 hours) after the first dose of antivenom; in four patients afibrinogenaemia lasted more than 24 hours. The dose of antivenom given before venom neutralisation ranged from one to 23 ampoules. In two-thirds of cases, venom was neutralised with five ampoules, and 89% had venom neutralised with 10 ampoules. Two patients died, and another had serious bleeding complications. Another patient died during the study period from intracerebral haemorrhage, but did not have fibrinogen levels measured. CONCLUSIONS Patients received initial doses of antivenom too small to neutralise circulating venom, and remained afibrinogenaemic for prolonged periods, with serious consequences. The authors now use 10 ampoules as an initial dose in severe brown snake envenoming.