This research work consisted in the assessment of the damaging effect of basic nitrogen in the performance of industrial catalytic cracking catalysts. Laboratory evaluation of an industrial equilibrium catalyst was done with four feedstocks with very distinct nitrogen contents: a gasoil with 1307 ppm of basic N (feedstock A); feedstock A after an acid treatment with the objective of partially removing the basic nitrogen (feedstock 13: 135 ppm of basic N); feedstock B after adding H 72 ppm of quinoline (feedstock C: 1307 ppm of basic N); and feedstock A after adding 1172 ppm of quinoline (feedstock D: 2479 ppm of basic N). Characterization of the gasoils showed that only the basic nitrogen content was affected by the acid treatment. The evaluation results showed that basic nitrogen reduces the gasoil cracking conversion in 5-10 wt% points, depending on the catalyst to oil ratio. In addition, at constant conversion, the increase in basic nitrogen content also resulted both in a decrease in gasoline yield and an increase in coke and hydrogen yields. Nitrogen contained in the quinoline molecule had similar effects to that present in the original gasoil. (c) 2007 Elsevier B.V. All rights reserved.