AbstractA differential pulse voltammetric method is presented for the determination of isopropylmethylphenols (carvacrol and/or thymol) in phytotherapeutic black seed oils. The voltammetric behaviours of these phenols were examined in various buffer systems over the pH range 3.5–10.0. In Sörensen buffered methanol solution (3:7; v:v; pH 8.5), the differential pulse voltammograms exhibited reproducible peaks at Ep + 0.49 V vs. silver–silver chloride–potassium chloride 3 m for both carvacrol and thymol. Under these conditions, a plot of peak height against concentration of the isopropylmethylphenols was found to be linear over the range 0.25–2.5 µg/mL (r = 0.999). The detection limit was 0.04 µg/mL. The described voltammetric method was tested on two black seed oils available on the Austrian market. Copyright © 2004 John Wiley & Sons, Ltd.