Aerobic and anaerobic culture of sputum on selective bacteriological media, combined with a new method of plating and plate reading, permitted rapid identification and quantitation of three genera of bacteria commonly associated with chronic bronchial sepsis (Haemophilus spp, Pseudomonas aeruginosa, and Staphylococcus aureus) and avoided time consuming serial dilution of sputum and subculture of organisms. The accuracy of this new technique was assessed in patients with chronic bronchial sepsis and was used to detect changes in the colonising microbial load of Haemophilus spp and Ps aeruginosa in patients with bronchiectasis receiving one of three different antibiotic regimens: intermittent seven day courses of amoxycillin for exacerbations; or a six month course of continuous oral or nebulised amoxycillin. The colonising microbial load of Haemophilus spp was reduced only temporarily (+++ to ++) after each intermittent course of antibiotic, but a sustained and greater reduction in the colonising microbial load of both Haemophilus spp (+++ to +) and antibiotic resistant P aeruginosa (+++ to +) was seen during both continuous treatments. Sputum purulence decreased in parallel with colonising microbial load, reflecting a reduction in host inflammatory response to the colonising microbial load.