SYNOPSIS. Cell‐free preparations from Crithidia jasciculata carried out protein synthesis as measured by 14C‐leucine uptake (optimum ∼ 10 mM Mg++) and poly U‐directed 14C‐phenylalanine uptake (optimum ∼ 16 mM Mg++). Characteristics of the system and sucrose density‐gradient patterns of ribosomes were investigated. The charging and transfer reactions—the 2 main steps in protein synthesis—were inhibited by stilbamidine, hydroxystilbamidine, pentamidine, quinapyramine (Antrycide), and suramin.