The nucleic acids (DNA and RNA) and total protein concentration in testes were estimated in male Wistar strain rats treated intraperitorally with nickel sulfate (2.0 mg/100 g body weight) on alternate days for 10 dosages. In both normal (18% casein) and protein-restricted (5% casein) experimental animals, the nucleic acids and total protein concentration were found to decrease significantly compared to the corresponding controls. Sperm count and sperm motility were also reduced in both experimental groups of animals. The results indicate that nickel influences the expression of genetic information by reducing testicular nucleic acids and protein concentration in both dietary experimental groups.