Human parasitic infestations of the skin by mites (Acari) and insects can be divided into permanent and temporary ectoparasitoses. This fact is important for diagnosis and treatment. Permanent ectoparasites are highly adapted to their host, the human being, and live in permanent contact with him. Diagnosis is usually simple and the parasite can be found on the patient. Treatment is by antiparasitic topical medication. In contrast to permanent ectoparasitosis, temporary ectoparasites are not found on the patient. When a bite reaction is perceptible the insect has left its host. The history of the affected patient is often very vague. However, some stinging insects are rather well known and are sometimes recognized by the patient or brought along for specific determination of the species. The bite reaction is not unique for the insects and does not allow an assumption regarding species diagnosis. The clinical manifestation of a bite reaction is dependent on the immunological situation of the host. Even more difficult is the diagnosis of temporary infestations by mites. Mites are very small and barely visible to the naked eye. Patients are unaware of the existence of mites and did not notice the infestation or the bite. In addition, mites will not be detectable in man at the time when the consequences of the infestation are perceptible. All in all, diagnosis appears to be very difficult. Suspicion may arise from history and the diagnosis must be confirmed by documenting the parasite on its primary host or in the environment of the patient. The treatment of the patient is unspecific against itch.(ABSTRACT TRUNCATED AT 250 WORDS)