The surface areas generated by the disintegration and dissolution of six commercial brands of phenylbutazone tablets B.P. 100 mg have been measured using a Model TA Coulter Counter. The graphs of surface area generated against time were all of the same shape and always reached a maximum value. The initial surface area increase was due to tablet disintegration and deaggregation and followed first order kinetics. A good correlation between the slope of this initial increase and disintegration time was found. The maximum surface area generated correlated at the probability level of better than 99-9% with the dissolution rat measured as t60. The subsequent decrease in surface area, after this maximum, was considered to be due to phenylbutazone dissolution and was also first order rate controlled.