We have tried to stress the complexity of the bacterial ecology that may exist in the intestine of patients and experimental animals with small intestinal bacterial overgrowth. The multiplicity of organisms often makes the management of these patients quite frustrating. A number of metabolic derangements of varying severity may occur in any given patient. Although many of the observed abnormalities are secondary to disturbed events with the luminal environment of the small intestine, the significance of direct damage to the small intestinal epithelium has been emphasized. Since intestinal cultures are both cumbersome and difficult to perform on a routine basis, the use of labeled substrate breath tests will allow guided, outpatient therapy more easily than in the past. Since full correction of the malabsorption is seldom achieved with antibiotic therapy, nutritional supplementation deserves more attention than it has previously received.