The finding by earlier workers that Escherichia coli suppressed the growth of Candida albicans in vitro or in gnotobiotic mice has led to numerous, erroneous conclusions regarding the identity of the organisms and mechanisms responsible for the suppression of Candida in the gut. This is due, in part, to the fact that nearly all studies to date have not reflected interactions as they occur in the intestinal tract. This paper describes a series of experiments that establish that an anaerobic continuous-flow (CF) culture model of the ecology of the large intestinal flora reproduces interactions between bacteria and Candida as they occur in the large intestine. This was determined in the following ways. (i) Bacterial counts in CF cultures of conventional mouse cecal flora or human fecal flora closely resembled that found in the mouse intestine and human feces. (ii) Dense layers of bacterial growth that formed on the glass walls of the CF culture vessels resembled bacterial populations that colonize intestinal mucosa. (iii) Total and individual levels of certain metabolic end-products of the predominant anaerobic bacterial flora present in CF cultures coincided with those found in the large intestine of conventional mice or human feces used to establish the CF cultures. (iv) C. albicans was eliminated from CF cultures of mouse cecal flora at a rate similar to that of untreated experimental animals. (v) Contents of CF cultures fed to antibiotic-treated mice redressed several cecal abnormalities, and suppressed Candida populations to levels found in conventional animals. Thus, a number of complex ecological mechanisms were maintained in CF cultures which normally control Candida populations in the large intestine. It is suggested, therefore, that the CF culture model should help to further define the mechanisms which control C. albicans and other fungi in the intestinal tract, as well as define which components of the indigenous microflora are responsible for suppression of Candida in the gut.