Bronchial inflammation is a consistent feature of asthma and its chronicity probably determines disease progression. Clinical evaluation of drugs with potential disease-modifying activity requires measurement of their effects on the inflammatory and remodelling process using a variety of techniques including bronchial biopsy, and analysis of sputum, bronchoalveolar lavage, blood, urine and exhaled air. Markers of the key components of the inflammatory process, such as the number and activation of T-cells. the number of mast cells, cytokine and chemokine release or gene expression, and eosinophil and neutrophil recruitment, can be determined in biopsy samples. Biopsies also allow assessment of the integrity and structure of the airway epithelium, the thickness of the reticular basement membrane and the numbers and ultrastructure of contractile cells. These and other markers may allow differentiation between subtypes of asthma patient according to atopic status and will help to distinguish asthma from chronic obstructive pulmonary disease. Airway remodelling may be a consequence of chronic bronchial inflammation and is a characteristic of chronic asthma, particularly in severe asthma and when there is progressive decline in lung function. There are changes in the surface epithelium, reticular basement membrane, bronchial smooth muscle, blood vessels and mucous glands. Reliable markers of remodelling need to be identified to improve our ability to evaluate chronic asthma therapy.