The effects of dimethoate (5, 15 and 28 mg kg(-1) day(-1)), deltamethrin (5 mg kg(-1) day(-1)) and their mixture (5 mg kg(-1) day(-1)) on male reproduction in mice were studied. The insecticides were given orally by gavage to male mice for 21 days. At the end of the treatment period, body, testes and epididymides weights and sperm parameters were determined. Alone mixture treatment has significantly decreased body weights. Dimethoate at 28 mg kg(-1) day(-1), deltamethrin at 5 mg kg(-1) day(-1) and their mixture at 5 mg kg(-1) day(-1) were associated with a significantly decreased sperm count, motility and viability and significantly increased percent morphologically abnormal spermatozoa compared with the controls. This study demonstrated the adverse effects of dimethoate at high dose, deltamethrin and their combining at 5 mg kg(-1) day(-1) on reproductive system and sperm parameters in male mice.