Three enzyme-linked-immunosorbent assays (ELISA) were developed and compared with a bioassay to quantify the recombinant human granulocyte-macrophage colony stimulating factor (rhGM-CSF). These assays were suitable to quantify the non-glycosylated rhGM-CSF present in mixtures with variable protein content, and therefore useful for determining concentrations of the cytokine in production processes. Among these assays, the competitive ELISA, developed with a MAb that recognises an epitope not involved in glycosylation, was the only one suitable to quantify the glycosylated form of rhGM-CSF produced in mammalian cell cultures.