EN
Magnetization M(T) and M(H) data of single crystals of the S=1/2 quasi-one-dimensional system (A_{2}Cu_{2}O_{3})_{m}(CuO_{2})_{n} with various A-site constituents are compared. The studied orthorhombic, incommensurate crystals are characterized by m/n=5/7,7/10, and 9/13. The role of rare-earth ions located in A-sites is discussed.