Two heavy forms (EF1H, mol. wt, 250 000) are found in cytosol while ribosome-bound factors contain a light form (EF1L, mol. wt, 45 000) with the greatest activity and a heavy form (mol. wt, 160 000) which might well be an intermediary in the recycling of ribosomal factor EF1L to soluble factor EF1H.