Kaiser effect was noticed while submitting marble samples to Brazilian tests. An automatic data acquisition system was applied by means of analog to digital conversion, upon recording analog signals of stress, strain and acoustic emission (AE) emitted from Portuguese marble specimens under diametrical loadings in different loading cycles. Results confirm that the Kaiser effect was pronounced and was easy to be detected under Brazilian tests with a felicity ratio varied from 0.92 to 1.09. This means it is possible to measure the pre-existing stresses in rocks under complex states of stress by means of other tests besides uniaxial compression. Results also show that cumulative AE events vs. stress curve is more suitable for Kaiser effect recognition than cumulative AE energy vs. stress curve as every event has different scales of energy.