We investigated the effect of Brussels sprouts, inulin and a fermented milk on the faecal microbiota diversity of human microbiota-associated (HMA) rats by PCR-temporal temperature gradient gel electrophoresis (PCR-TTGE) using universal and group-specific 16S rRNA gene primers. The HMA rats were submitted to a control diet for 10 d (initial time), then switched to the experimental diets for 4 weeks (final time). Using universal primers, the mean degree of similarity between all faecal samples at initial time was 80·8 %. In the group consuming the control diet throughout the experiment, the mean degree of similarity between the PCR-TTGE profiles at initial v. final time was 76·8 %, reflecting a spontaneous temporal variation. The mean degree of similarity between control and experimental groups at final time was lower, 72·4 %, 74·4 % and 75·6 % for inulin, Brussels sprouts and fermented milk, respectively, indicating a dietary effect on the predominant populations. Using specific primers, bifidobacteria could be detected only in those rats that had consumed inulin, showing a specific increasing effect of this dietary compound. The Lactobacillus population was very heterogeneous at initial time but tended to homogenize within each dietary group. At final time, caecal contents were collected for analysis of SCFA and β-glucuronidase activity. Inulin and Brussels sprouts increased the butyrate and acetate proportion, respectively, while the fermented milk did not modify the caecal biochemistry. This experiment shows for the first time that cruciferous vegetables are able to alter the diversity and the metabolic activities of the digestive microbiota in HMA rats.