Rationale: Markers of inflammatory activity are important for assessment and management of many respiratory diseases. Markers currently unrecognised may be more valuable than those presently thought useful. Objective: To identify potential biomarkers of suppurative and inflammatory lung disease in induced sputum samples. Methods: Induced sputum was collected from 20 healthy controls, 24 patients with asthma, 24 with COPD, 28 with Cystic Fibrosis (CF) and 19 with bronchiectasis. 12 CF patients had sputum sampled before and after antibiotic therapy for an infective exacerbation. The fluid phase of induced sputum was analysed by SELDI-TOF mass spectroscopy on three protein array surfaces. Some protein markers were selected for identification, and relevant ELISA assays sought. For 12 CF patients both SELDI-TOF and ELISA monitored changes in inflammatory responses during infective exacerbations. Main Results: SELDI-TOF identified potential biomarkers that differentiated each of the disease groups from healthy controls: at a significance of P<0.01 there were 105 for asthma, 113 for COPD, 381 for CF and 377 for bronchiectasis. Peaks selected for protein identification yielded calgranulin A, calgranulin B, calgranulin C, clara cell secretory protein, lysosyme c, proline rich salivary peptide, cystatin s and haemoglobin alpha. On treatment of an infective CF exacerbation SELDI-TOF determined falls in levels of calgranulin A and calgranulin B that were mirrored by ELISA measured falls in calprotectin (heterodimer of calgranulins A and B). Conclusions: Proteomic screening of sputum yields potential biomarkers of inflammation. The early development of a clinically relevant assay from such data is demonstrated.