[Unusual Koebner phenomenon in psoriasis caused by varicella and UVB].

An isomorphic response is defined as a nonspecific skin stimulus eliciting a disease-specific skin reaction. We report on the development of the Koebner phenomenon in a 32 year old patient with psoriasis after skin testing with UVB at a dose above 0.055 J/cm2. In addition we describe a 28 years old patient who developed new psoriatic plaques in the areas affected by the virus after a varicella infection.