We examined the physiological importance of bovine dietary proteins in rats fed diets prepared from bovine Achilles' tendons and arteries. Rats were fed for 4 weeks, with a 20 % casein diet (CON), in comparison with two diets containing 15 % casein and 5 % of either bovine Achilles' tendon (AC) or artery (AR) protein preparations. The serum total cholesterol concentration and non-HDL-cholesterol level in the AR-fed group were significantly lower (P < 0·05) than those in the CON-fed group at the end of the 4-week feeding period. The hepatic mRNA were measured, and the hydroxyl methyl glutaryl-CoA reductase mRNA level was significantly lower (P < 0·05) in the AR-fed group compared with the CON-fed group. Total hepatic cholesterol concentration in AC-fed rats was significantly (P < 0·05) higher than in the CON-fed group. The serum TAG concentration and fatty acid synthase mRNA level in AC- and AR-fed groups were significantly lower (P < 0·05) compared with the CON-fed group throughout the feeding period. Faecal neutral sterol excretion was significantly (P < 0·05) higher in the AC- and AR-fed groups compared with the CON-fed group. The results of the present study demonstrate that some bovine dietary proteins have similar functions as dietary fibres, lowering serum lipid concentration by enhancing faecal neutral sterol excretion or suppressing lipid synthesis in the liver. Moreover, favourable amino acid compositions in the AR and AC preparations may also have a lowering effect on plasma lipid concentration in bovine protein diet-fed groups.