Testicular torsion is a well-known medical emergency that can lead to pathological changes in the testicular tissues and male infertility. This investigation was undertaken to gain insight into the effects of an endothelin type A receptor antagonist (BQ123) on torsion-induced germ cell loss. Twenty-eight male Wistar albino rats were divided into four groups. In group I (control group), a sham operation to the left testis was performed. In group II (I/R injury), I/R injury was created by rotating the left testis 720 degrees in a clockwise direction for 2 h and detorsing the testis after 2 h. In group III (I/R injury+BQ123), the rats were subjected to I/R injury and BQ123 injection (1 mg/kg, intravenous). In group IV (control+BQ123), the sham operated rats were subjected to BQ123. The testes of the rats were removed in all groups. Torsion-induced apoptosis and the effects of BQ123 were examined by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end labelling (TUNEL) technique, immunohistochemistry and western blotting. In group II, the number of TUNEL-positive cells increased after testicular torsion. Immunohistochemistry and western blotting showed that apoptotic proteins (active caspase 3 and Bax) were upregulated, and the anti-apoptotic protein Bcl2 was downregulated in I/R injury. The administration of BQ123 caused a significant decrease in the number of apoptotic cells and the expression of apoptotic proteins (p<0.05) when compared with the I/R injury group. No significant effect of BQ123 was observed in the testicular cells of group IV. This animal study provides evidence of the regulatory effects of BQ123 on torsion-induced testicular apoptosis.