Changes of concentrations were studied in water buffaloes and goats infected with Fasciola he-patica on blood NO(nitric oxide) and TNF-α(tumor necrosis factor-α). Twenty healthy male castrated waterbuffaloes of 2 - 3 years old and weighing 300 - 500 kg as well as six goats were confirmed free of fasciolosis byfecal examination and Dot-ELISA. Two studies were conducted using the water buffaloes. In the first experi-ment, 8 water buffaloes were randomly divided into control group (n=3) and infection group (n=5). Eachbuffalo in the infected group received orally 60 metacercariae of F. hepatica per day for 20 days (total 1 200metacercariae) to produce a chronic infection. In the second experiment, 12 water buffaloes were randomly di-vided into infected (n=9) and control group (n=3). Each buffalo in the infected group was given a singleoral dose of 1 600 metacercariae to produce an acute infection. The 6 goats were randomly divided into two in-fected groups and a control group. The sheep in two infections received a single oral dose of 200 and 500 meta-cercariae respectively, the control group remained uninfected. Blood NO and TNF-α concentrations of the testanimals were measured by a reductive enzyme assay and RIA, respectively. Blood NO concentration in bothacutely and chronically infected water buffaloes progressively increased from week 3 post-infection and was sig-nificantly greater than that of the control group (P＜0.05) at the 5th week (acute infection) and 7th week(chronic infection), and remaining at higher concentration for the remaining period of the studies. BloodTNF-αt concentrations in both chronically and acutely infected water buffaloes also increased after infection. Inthe goat experiment, plasma NO concentrations in both infection groups increased from week 3 after infection,and remained higher than that of the control group until the end of the experiment. TNF-α concentrations ingoats in infection group 1 and 2 gradually increased after infection and were significantly greater than those ofthe control group from the 9th to 11th week and from the 11th to 15th week respectively.