A long-acting pegylated form of a recombinant therapeutic agent which is chemically identical to or similar to an endogenous human granulocyte colony-stimulating factor (G-CSF). Produced endogenously by monocytes, fibroblasts, and endothelial cells, G-CSF binds to and activates specific cell surface receptors, stimulating neutrophil progenitor proliferation and differentiation and selected neutrophil functions. Conjugation of the cytokine with a branched polyethylene glycol molecule (pegylation) significantly increases its therapeutic half-life.