A comparison of the absorption and incorporation of C(14)-proline into protein by the 7 kinds of helminth parasites is presented. The radioactivity of free amino acid fraction is greater than that of protein fraction in all the worms, and only a small amount of exogenous labeled proline is incorporated into tissue protein. In general, the pattern of C(14)-proline uptake and its incorporation into protein shows rapid linear increase during the period of 15 to 30 min and reaches the maximum at 60 min after incubation, and then the equilibrium state was maintained throughout further incubation.