In 79 patients, with carcinoma of the oesophagus, oesophageal aspirates obtained at oesophagoscopy were cultured for aerobic and anaerobic organisms in an attempt to identify the microbial flora. The aspirate culture was correlated with the pathogens isolated when infective complications developed after operation. Bacteroides were isolated from the oesophagus in 39.2% of patients, streptococcus in 10.1% and coliform organisms in 7.6%. No growth was obtained in 35.4% patients. Forty-one patients underwent oesophageal resection. Six of these had the complication of empyema thoracis in the postoperative period. Two patients had identical organisms isolated from the oesophagus and the empyema. B. melaninogenicus was cultured from the pleural fluid in two patients whose oesophageal aspirate culture yielded no growth. Six patients developed wound infection, all with anastomotic cutaneous fistula. There was no demonstrable relationship between the organisms isolated from two sources. Prophylactic antibiotic administration should be directed against the bacteroides, since it is the most common organism isolated from within the oesophagus.