Three patients with chronic urticaria or pruritus were found to suffer from an asymptomatic intestinal infection caused by the protozoan Giardia lamblia. Treatment with metronidazole per os or tinidazole per os was successful; the pruritic symptoms in one patient improved markedly.Giardia lamblia (Giardia intestinalis) are enteroparasites and produce gastrointestinal symptoms such as acute and chronic diarrhea. Cutaneous manifestations associated with giardiasis occur extremely rarely. Urticaria and itching may be explained as an infection-associated allergy. Hitherto, the following cutaneous signs have been described: urticaria, angioedema, mouth ulcers, pruritus, atopic dermatitis, and anal eczema.We considered that the cutaneous manifestations described here, i. e., urticaria and itching, were secondary to the associated gastrointestinal infection due to Giardia lamblia cysts and trophozoite forms, as they disappeared under specific treatment with metronidazole or tinidazole.