Water-soluble composition for sustained-release

A water-soluble parenteral composition for injection which comprises (a) a water soluble pharmacologically active peptide selected from the group consisting of cytokines or hematopoietic factors, and (b) an alkali metal salt of a sulfate group-containing acidic mucopolysaccharide and/or a desulfated modification of a naturally occurring sulfate group-containing acidic mucopolysaccharide, wherein the weight ratio between (a) and (b) is about 0.001 to about 1:1, and wherein prior to injection, the tonicity and viscosity of the composition are adjusted by the addition of sterile water or sterile saline, to obtain a solution such that the viscosity of the solution is lower than 500 cP and the tonicity of the solution is from one-half to twice as high as that of physiological saline.