An isomorphic response is defined as a nonspecific skin stimulus elici
ting 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/cm(2). In addition we de
scribe a 28 years old patient who developed new psoriatic plaques in t
he areas affected by the virus after a varicella infection.