Abstract: A 75 day study was conducted comparing the anticoccidial efficacy of monensin and Yucca schidigera saponins (YS) in calves with naturally infection. A total 27 beef cattle selected for body weight and degree of oocysts shedding were allocated to three groups of 9 animals each: MON (Monensin, 140 mg/animal/day), YS (Yucca schidigera saponins, 15 g/animal/day) and CTRL (non-treated control). Individual faecal samples were collected at day 0, 15, 30, 45 and 75 to evaluate oocysts excretions (OPG), faecal consistency score and dry faecal percentage; body weight was recorded at day 0 and 75. On day 15, OPG were significantly lower in YS and MON compared to CTRL (p = 0.014 and 0.017, respectively). From day 30 to the end of the study, OPG values were similar in all groups and a complete coccidial elimination was not recorded in any group. Faecal scores and dry-faecal percentages did not differ significantly between groups throughout the study. The highest mean daily weight gain was recorded for MON (1.73 kg/hd/day) with respect to YS (1.45 kg/hd/day) and CTRL (1.32 kg/hd/day). This study suggests that Yucca schidigera saponins under conditions of natural exposure to coccidiosis and normal management practices have anticoccidial activity and that a little advantage in gain can be obtained.