The formation of coke on sulfated zirconia during the isomerization of n-butane was quantified as a function of time on stream and temperature. The formation of coke was essentially linear with time on stream when the isomerization reaction was performed at 200 degrees C. When the amount of coke deposited reached 0.04 wt.%, the catalytic isomerization activity was observed to decrease to 10% of its initial value. When the reaction temperature was increased, the higher selectivity to cracked products resulted in an increase in coke formation and a higher rate of deactivation. The deactivated sulfated zirconia catalyst could be completely regenerated in air at 450 degrees C. The TGA/FT-IR technique used offers significant advantages over other methods of quantifying coke deposition.