Acanthocheilonema viteae,Litomosoides cariniiandSetaria cerviwere found to actively synthesize proteinsin vitro. Different centrifugation fractions and their TCA-precipitable fractions were assessed for the distribution of newly synthesized proteins. Penicillin and streptomycin inhibited the process inA. viteae. The synthesis inS. cerviwas susceptible to puromycin, chloramphenicol, cycloheximide, neomycin and polymyxin B. The process inL. cariniiwas strongly blocked by puromycin while chloramphenicol had no significant effect.