The effect of microwave‐ and oven‐baking on residues of the postharvest fungicide thiabendazole (E 233) in potatoes was investigated by comparing amounts present in raw, microwave‐ and oven‐baked tubers. The levels of residues in the whole potato tubers were based on the determination of thiabendazole in peelings and flesh of potato tubers by reversed‐phase HPLC analysis with fluorescence and UV detection after extraction with dichloromethane in the presence of anhydrous sodium sulphate. Amounts of thiabendazole determined after microwave‐ and oven‐baking showed that thiabendazole was predominantly retained in the peelings (96.3–98.8%) and not lost during the two types of processing treatments atca.100°C. Thus residues did not migrate into the flesh of the tubers.