Objective of the study was to determine whether L.rhamnosus strains (573L/1; 573L/2; 573L/3) enclosed in the preparation Lakcid L®, have an influence on acute diarrhea in children from 2 m. to 6 y. old. Randomized, double-blind, placebo-controlled trial was performed. Primary outcome measure was the diarrhea duration. Secondary outcome measures were: weight gain, no. of stools in consecutive days, duration of parenteral rehydration, diarrhea lasting over 7 days and GI tract colonization by administered strains. 93 patients were enrolled to the study. Children were treated according to ESPGHAN recommendation and additionaly , they received either 1.2 1010 CFU mixture of L. rhamnosus strains or placebo twice daily for 5 consecutive days. Results: 87/93 (93,5%) patients were analyzed. 46/87 (52,9%) children were in probiotic group and 41/87 (47,1%) were in placebo group. 39/87 (44,8%) had rotaviral infection (22 recived Lakcid L, 17 recived placebo. Mean duration of diarrhea in the treated group: 83.6 ± 55.6 h; in placebo group: 96 ± 71.5 h (p=0,36). In rotavirus infection: 77.5 ± 35.4 h vs 115 ± 66.9 h (p=0,03), respectively. Duration of parenteral rehydration 14.9 ± 13.7 h vs 37.6 ± 32.9 h; (p=0,006). The applied probiotic strains were detected in stool samples of 37/46 (80.4%) children in 5 days and in 19/46 (41.3%) samples in 14 days after initiating the treatment. Conclusions: Lakcid L administered orally in dose 1,2x1010CFU twice daily for 5 consecutive days has no influence on diarrhea of any etiology but shortens the duration of rotaviral diarrhea in children which is probably related to succsessful gut colonization.