HIV/AIDS is an infection characterized by immune cell dysfunction and subsequent immunodeficiency, as well as intestinal disorder. Probiotics are live microbial feed supplements that beneficially affect the host animal by improving intestinal microbial balance and promoting health benefits. The goals of this study were to determine whether the use of probiotics could improve the immune response determined by CD4 cells mm(-3) counts and reduce liquid stool episodes. A randomized double-blind controlled trial with 77 HIV-infected children (2-12 years), divided into two groups: one receiving probiotics (formula containing Bifidobacterium bifidum with Streptococcus thermophilus -2.5 x 10(10) colony forming units) and the other, a standard formula (control group), for 2 months. The CD4 counts (cells mm(-3)) were collected at the beginning and end of the study. The quality and number of stools were assessed by a questionnaire (watery to normal stool consistency). There was an increase in the mean CD4 count in the probiotics group (791 cells mm(-3)) and a small decrease in the control group (538 cells mm(-3)). The change from baseline in mean CD4 cell count was +118 cells mm(-3) vs. -42 cells mm(-3) for children receiving the probiotic formula and control formula, respectively (p = 0.049). A similar reduction in liquid stool consistency in both the groups (p < 0.06), with a slight enhancement in the probiotics group, was observed, but without significant difference (p < 0.522). The incidence of loose-soft stools showed a small decrease in both groups (p < 0.955) and there was an increase in the incidence of normal stool consistency in both the groups (p < 0.01). Our study showed that probiotics have immunostimulatory properties and might be helpful in the treatment of HIV-infected children.