Airways inflammation markers may help in predicting prognosis, in diagnosis and in monitoring respiratory diseases. Inflammation markers specific for certain cells may indicate the nature of the inflammatory processes, whilst others indicate stage and intensity. Intercellular adhesion molecule 1 (ICAM-1) helps to establish contact between the antigen-presenting cell and T-lymphocytes. Soluble serum ICAM-1 is increased in developing chronic lung disease of the newborn and atopic bronchial asthma. ICAM-1 is also the major human rhinovirus receptor. Interleukin 4 and interferon-gamma regulate the immunoglobulin E response, are difficult to measure in serum, and most groups employ stimulated cell cultures. These early inflammation markers may have predictive value. The leukotrienes are released from mast cells and eosinophils. Leukotriene (LT) B4 may be analysed in serum, whereas the cysteinyl leukotrienes, LTC4, LTD4, LTE4, may be assessed in urine. Serum LTB4 and urinary LTE4 have been found to be elevated during acute wheezy exacerbations. Tryptase is released from mast cells and is elevated in serum during acute anaphylaxis. However, tryptase has not been found to be related to inflammatory activity under other conditions. Myeloperoxidase is released from neutrophils, and serum levels are elevated in asthma, respiratory infections and other chronic lung diseases. The eosinophil markers eosinophil cationic protein (ECP) and eosinophil protein X (EPX) reflect eosinophil activation. ECP in serum and EPX in urine are elevated in asthma, atopic eczema and other conditions with eosinophil activation. They are related to symptom activity in asthma and atopic eczema and are influenced by anti-inflammatory therapy. In early wheezing, serum ECP may have predictive value. Serum ECP is dependent upon sampling procedures. Nitrogen oxide in exhaled air reflects inflammatory activity in asthma, and is influenced by anti-inflammatory therapy. However, in young children there are sampling difficulties.