The jejunal flora of 15 patients with megaoesophagus secondary to Chagas disease was studied and compared with that of 15 control individuals. In addition to the serological reactions for Chagas disease (immunofluorescence and complement fixation reaction), all subjects were submitted to endoscopy and X-ray of the oesophagus, gastric secretory study and investigation of the jejunal flora. The mean bacterial counts (log10) of Chagas disease patients (4.14 +/- 2.15 c.f.u./ml) was significantly higher than those of the control group (2.83 +/- 1.34 c.f.u./ml). Aerobic bacteria were isolated from 14 Chagasic patients (maximum count 10(10) c.f.u./ml) and 7 controls (maximum count 10(5) c.f.u./ml). Anaerobes were isolated from 7 patients (maximum count 10(7) c.f.u./ml) and 1 control (10 c.f.u./ml). Controls and Chagas disease patients differed significantly in the maximum acid output, but there was no statistically significant relation between bacterial counts and maximum output.