A chromatographic method was developed to detect and confirm the presence of succinonitrile (SDN) in horse urine samples, for antidoping control. The urine samples (5 ml) were extracted with diethyl ether and screened by gas chromatography–nitrogen–phosphorus detector and the confirmation of the drug's presence was accomplished by using gas chromatography–mass selective detection. The recovery of extraction was 78 and 81% for 1.0 and 2.0 µg ml^–1(relative standard deviation, <10%), respectively. Urine samples collected after the administration of Energisan were positive for SDN (1–30 h) in all samples analysed.