Granulocyte-macrophage colony stimulating factor (GM-CSF) is an important hematopoietic growth factor which has been shown to induce proliferation and activation of inflammatory cells and may play a role in allergic diseases. An activity of GM-CSF was determined in serum and BAL-fluid of 12 asthma patients with bronchial hyperreactivity to histamine before and 24 hours after challenge test. It was found statistically significant increase (p < 0.05) of GM-CSF activity in patients with bronchial hyperreactivity to histamine.