The bioavailability of an improved formulation of enteric-coated phenylbutazone with faster dissolution, more consistent in vitro rate of drug release and improved stability was compared in 8 normal subjects at doses of 100 and 200 mg with commercially available Butacote. Phenylbutazone was more rapidly absorbed from the new formulation and higher plasma concentrations were achieved at shorter intervals after dosing. Drug elimination rate was unaffected by reformulation and despite faster absorption the total amounts of drug reaching the circulation from the new and commercial products were similar. It was concluded that replacing Butacote by the new formulation would provide the same therapeutic benefit.