Qualitative and quantitative sputum cytologic and bacteriologic variables were determined in 38 patients with chronic bronchial disease. In each of 60 infectious exacerbations, three distinct periods were examined: stable phase (SS), bacterial (acute infections) exacerbation (AIE), and post-infection (PI). The neutrophil and histiocyte represent nonspecific cellular host defense but demonstrate different response patterns. Neutrophils increase significantly during AIE but return to SS levels by Pl. Histiocytes remain low during AIE but are elevated during Pl. Bronchial epithelial cells parallel the neutrophil change in AIE but do not return to SS levels by Pl. These measurements, along with the in vivo phagocytic indices (neutrophils and histiocytes with bacteria) and the infectivity index (bronchial epithelial cells with bacteria), provide direct objective criteria for evaluating the cellular dynamics of host defense in bronchopulmonary diseases.