The testosterone levels decreased by T-2 toxin in mouse Leydig cells were reported previously. It is not known, however, whether L-arginine improves the situation and what's the mechanism. Leydig cells were isolated and cultured with control, 10 nM T-2 toxin, 0.25, 0.5 or 1.0 mM L-arginine, and 10 nM T-2 toxin supplemented with 0.25, 0.5 or 1.0 mM L-arginine for 24 h. Cells and supernatants were collected to detect the mRNA expression and activities of P450scc (cholesterol side-chain cleavage enzyme), 3 beta-HSD-1 (3 beta-hydroxysteroid dehydrogenase/isomerase-1) and StAR (steroidogenic acute regulatory protein). Results revealed that L-arginine increased the testosterone levels declined by T-2 toxin and up-regulated the activities and mRNA expression of P450scc, 3 beta-HSD-1 and StAR down-regulated by T-2 toxin in Leydig cells. Therefore, we concluded that L-arginine ameliorated the testosterone levels decreased by T-2 Toxin via regulating the mRNA expression and activities of P450scc, 3 beta-HSD-1 and StAR in mouse Leydig cells. (C) 2019 Elsevier Inc. All rights reserved.