Cadmium (Cd²(+)), a naturally occurring heavy metal, is an important environmental pollutant and a potent toxicant to bacteria. The gastrointestinal (GI) tract microflora has a marked capacity to cope with the increased load of ingested metals. However, heavy metals may have harmful effects on GIT microflora. Under the conditions of experimental exposure to cadmium, changes in the population of intestinal microflora in healthy mice were examined. Five experimental groups received 23 to 50 mg kg⁻¹ cadmium in drinking water and control group was given water free from cadmium for 45 days. Intestinal contents and biopsy samples were aseptically collected and bacterial counts were performed. The microflora of the intestine in control group was represented by bacteria of the genera Bacillus cereus, Lactobacillus spp., Clostridium spp., Escherichia coli, Klebsiella spp., Pseudomonas spp., Enterococcus spp. and Proteus spp. As the result of dysbiosis induced by the introduction of cadmium, a sharp decrease in the population of all microbial species in the intestine was observed. The deleterious effect of cadmium appeared to be less in the large intestine and rectum than that of small intestine, suggesting a site-specific influence of cadmium. The gram-negative bacteria tested were less sensitive to cadmium compared to the gram-positive bacteria because of their possible different ability to uptake the metal ions.