BACKGROUND: Stanozolol and Nandrolone decanoate are the most commonly used hormones in canine medi-cine. They are mainly administered to strengthen the muscle, gain weight, treatment of anemia and stimulate the appetite. One of the effects of hormones is to enhance the erythropoietin production and eventually an increase in the number of RBCs. OBJECTIVES: Prolonged usage of hormones may be relevant to the liver and renal disorders; therefore, the pre-sent survey was aimed to evaluate the effects of stanozolol and nandrolone decanoate on liver and kidney indices, erythropoietin and testosterone serum concentrations and hematocrit changes in healthy dogs. METHODS: Sixteen dogs were randomly categorized in two groups of A (stanozolol) and B (nandrolone decano-ate). Each group was divided into two subgroups (A1, A2 and B1, B2). The second testicle was removed on day 28 in the first subgroups (A1 and B1), and day 42 in the second subgroups (A2 and B2). The first testicle was removed at time zero. Stanozolol (50 mg per dog) was administered to all dogs of group A as IM once a week for six weeks. Group B was similar to group A with the difference that nandrolone decanoate was injected (1 mg/kg) instead of stanozolol. Blood samples were collected on days 0, 3, 14, 28 and 42. RESULTS: Erythropoietin and testosterone concentrations were virtually increased in both groups A (p <0.05) and B (p <0.05). The effect of stanozolol on erythropoietin (subgroup A1) (11.35±1.31 ng/mL) was significantly higher than nandrolone decanoate (subgroup B1) (8.02±0.55 ng/mL) (p <0.05); nevertheless, the changes in testosterone levels, was not significant between groups A and B (p >0.05). The liver enzymes of ALP, ALT and AST were increased more significantly in group A than group B (p <0.05). CONCLUSIONS: Erythropoietin and testosterone levels were virtually increased in both groups A and B; how-ever, stanozolol had more significant effect than nandrolone decanoate in increment of erythropoietin; nevertheless, it had more side effects on liver indices. It is suggested that nandrolone decanoate to be administered for the thera-peutic goals.