The results of a clinic assay with an extract made out of propolis (bee glue) or "Propolisina" were showed with the aim of showing its effectivity against giardiasis. One hundred and thirty eight patients were studied 48 children and 90 adults, in 2 groups and they selected aleatorily to be treated with "Propolosina" or an imidazole derivate (tinidazole). The method for an exact diagnosis in children was duodenal aspiration and in adults duodenal mucosa frotis by means of duodenoscopy. Similar studies were carried out as a cure criterium in a 5-day term after being through with the treatment. Propolisina was used with different concentrations: in children (concentration at 10%) results showed a 52% cure. In 40 adults (concentration at 20%) it was obtained a similar result to that of tinidazole; and when propolisina concentration was elevated at 30% in the remaining 50 patients there was a higher effectivity (60 of cure Vs 40% with tinidazole). This work shows the success of this natural product, which is very easy to obtain in Cuba and with no side effects in the treatment of this intestinal parasitism, what is of great economical importance for our countries.