The effects of two levels of infection with 20 and 50 cysticercoids ofRaillietina tetragona (Cestoda) on certain aspects of protein metabolism of White Leghorn chickens were studied for a period of 8 weeks post-infection. Infection had no effect on the total protein content of liver while that in intestinal tissues was slightly reduced. The free amino acid nitrogen in the blood was not altered during infection. The serum total proteins and the serum albuminglobulin ratio were reduced significantly in infected birds. The hypoproteinemia was mainly due to the hypoalbuminemia. The infected birds gained significantly less weight than the uninfected ones. The lowered serum proteins is correlated with the lowered weight gain. Pathological changes were more pronounced in birds infected with 50 cysticercoids and during the period from 4 to 6 weeks post-infection.