Previous studies have reported that repeated administrations of linear gadolinium-based contrast agents lead to their accumulation in the brain and other tissues in individuals with normal renal functions. The purpose of this prospective animal study was to investigate the effect of multiple administrations of macrocyclic ionic (gadoteric acid) and linear nonionic (gadodiamide) gadolinium-based contrast agents (GBCAs) on rat testis tissue and to compare these molecules in terms of tissue damage. Thirty-two male Sprague-Dawley rats were kept without drugs for 5weeks after administration of 0.1mmol mg(-1) kg(-1) (0.2ml/kg) gadodiamide and gadoteric acid for 4days over 5weeks. Biochemical, histopathological and immunohistochemical changes in testis tissue were evaluated at the end of 10weeks. When used in repeated clinical doses, gadolinium was observed to increase apoptosis in the Leydig cells of the rat testis, and to increase serum Ca+2 levels and reduce testosterone levels (p<.05). Although the difference was not statistically significant, a greater loss of spermatozoa and immature germinal cell accumulation were observed in the seminiferous tubule lumen in the GBCA groups compared with the control and saline groups (p>.05). Both linear and macrocyclic contrast agents have toxic effects on testis tissue, irrespective of the type of drug.