BACKGROUND: Coronary artery spasm is among the etiology of myocardial infarction. Oxidative stress is involved in the pathogenesis of coronary artery spasm (CAS). Paraoxonase-1 (PON1) is an HDL-bound antioxidant enzyme that protects LDL from oxidative modification. Oxidative-stress-related genetic factors and certain polymorphisms in the paraoxonase 1 gene might influence the pathogenesis of CAS. We aimed to investigate the association between PON1 gene polymorphism and its enzymatic activity and coronary artery spasm during cardiac catheterization. METHODS AND RESULTS: The study population was 150 patients who underwent elective coronary angiography. Subjects were genotyped to the Q192R polymorphism (rs662) on the PON1 gene by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), and PON1 activity was quantitatively analyzed by enzyme linked immunosorbent assay. Results showed that the subjects carrying the RR genotype and R allele were significantly more likely to develop coronary artery spasm (OR=4.2, 2.03, CONCLUSION: We conclude that the PON1 (rs662) gene polymorphism is associated with CAS during cardiac catheterization in Egyptians. The PON1-192R allele and lower serum enzyme concentration may play an important role in coronary spasm.