Resistance is a practical problem associated to the use of benzimidazoles in the antigiardial therapy. Since benzimidazole-resistant strains of fungi have shown increased sensitivity to phenylcarbamates, in this study we synthesized and in vitro tested novel substituted phenylcarbamates against the protozoa Giardia intestinalis. IRE-6A and IRE-7B, two 4-R-ethyl-phenylcarbamates demonstrated an important antigiardial activity although that was modest when compared to albendazole in axenic cultures of Giardia intestinalis. Results of this study suggest a potential role of phenylcarbamates as alternative to benzimidazoles in the therapy of giardiasis.