Biological response modifiers (BRMs) of current clinical interest may be divided into two categories: immunomodulating agents and colony stimulating factors (CSFs). The first are employed to potentiate the host defences towards the tumor but results have proved disappointing in non-small cell lung cancer (NSCLC). With regard to the second, the real dose increment which may be ascribed to CSFs is not sufficient to overcome chemoresistance of NSCLCs. CSFs can, however, reduce the hematologic toxicity of chemotherapy, which represents the most significant result.