The increasing demand for a quick and simple screening tool of FCC catalysts and feedstocks has propelled the well known micro-activity test (MAT) ASTM-D 3907-80 far beyond its original purpose. Where once this test was a tool for assessing the catalyst activity, it is now routinely used to predict the yields in commercial FCC units, However, the necessity of a thorough revision of this test is generally agreed upon to come up to its new requirements. To obtain data reflecting those observed in circulating riser pilot units, which provide the best smaller-scale simulation of commercial FCCU operation, a new MAT method was developed using an operating scenario quite different from those of the traditional ASTM-MAT test. Cracking of vacuum gas oil and heavy resid feeds over catalysts with quite different properties was performed with the ASTM-MAT technique, the modified MAT approach and in a riser pilot unit to evaluate the modified procedure, This paper shows that with the choice of appropriate experimental conditions for MAT, a good simulation of the riser pilot units can be obtained. It is demonstrated that the modified test eliminates the ranking reversals identified for the comparison of catalyst selectivities obtained by the ASTM-MAT and riser pilot units. Moreover the selectivity levels obtained by the modified MAT configuration are very close to riser data indicating similar reaction pathways in these very different reactor types.