A reverse~phase hlgh-performance liquid chromatographic technique with isocratic elution has been developed to separate and quantitate the major phenolic compounds of the hydroalcoholic extracts of olive oils. Hydroxytyrosol, tyrosol, caffeic acid, phydroxyphenylacetic acid and homovanillic acid were analyzed on a pBonapak C18 column with an acetonitrile/water/acetic acid (20:90:0.18, vol/vol/vol) mixture as a mobile phase. Electrochemical detection provided selectivity as well as sensitivity. The method was applied to the analysis of the most important phenolic compounds in olive oils. KEY WORDS: Caffeic acid, electrochemical detection, HPLC, homovanillic acid, hydroxytyrosol, olive oil, p-hydroxyphenylacetic acid, tyrosol.HPLC-electrochemical analysis. Twenty ~_L of each sample was injected onto the column through an ALTEX 210 A injection valve (Beckman Instruments Inc., Berkeley, CA) equipped with a 20-mL sample loop. The sensitivity