The purpose of this study was to investigate cognitive changes in hyperlipidemic patients by means of spectral parameters of event-related brain potentials (ERPs). ERPs of 20 hyperlipidemic patients and age-matched healthy controls were elicited using infrequent and frequent stimuli in the form of red and green lights, respectively. The inferequent stimulus had a 15% probability. ERPs were recorded under two different experimental conditions: one where the infrequent stimulus was counted (Test 1) and one where it was uncounted (Test 2). Amplitude spectra of ERPs were computed with the transient response-frequency characteristics (TRFC) method. Their maxima were observed in the frequency bands 1-2, 3-4, 5-7, 8-12, 13-20 and 20.5-32 Hz.The amplitude means (decibel) of the 1-2 and 3-4 frequency bands were decreased in Test 2 in comparison with Test 1 in the control group, but no amplitude differences were found between Test 1 and Test 2 in the hyperlipidemic group.