AbstractThe programme of protein synthesis accompanying cellular differentiation to the heterocyst following transfer of the blue‐green algaeAnabaena circularisandCylindrospermum sp. (CBSC 1755) from ammonia‐enriched medium to nitrogen‐free medium was determined by polyacrylamide gel electrophoresis of whole proteins during successive intervals of differentiation. Besides this, total proteins and soluble amino acids were determined quantitatively. At least 4 sets of proteins can be distinguished on the basis of the time at which they are synthesized. Besides this, differentiation is distinguishable on the basis of the time at which their synthesis is turned off. The postmaturation stages revealed the synthesis of two sets inA. circularisand one inCylindrospermum sp. (CBSC