USING principal component analysis, we studied trial to trial, spontaneous variability of evoked potentials (EPs) recorded from rat barrel cortex after whisker stimulation. This method allowed for extraction of two distinct components of EP which overlapped in the time domain. Our results are consonant with the previously described depth distribution of current sources and the extracted components can be therefore attributed to activities of two pyramidal cell classes: supra- and infragranular. Qualitatively similar results were found in both anaesthetized and alert animals.