Free and membrane-bound polysomes were isolated from the protozoa Tetrahymena pyriformis, and the contribution of these two types of polysomes to tubulin synthesis were studied using immunoprecipitation of the 35S-translational products in a rabbit reticulocyte lysate. One-dimensional electrophoretic analysis shows that tubulin is synthesized by polyadenylated RNA isolated from free and membrane-bound polysomes. Non-polyadenylated RNAs of free polysomes are also able to direct tubulin synthesis. Two-dimensional electrophoretic analysis using O'Farrell's system confirms these results and also reveals the existence of the alpha- and beta-tubulin subunits.