Study on two different irradiation schemes in UVB phototherapy for psoriasis. Previous studies demonstrated a similar clinical effect in erythematogenic and suberythematogenic irradiation, with less complications in suberythematogenic irradiation. Most of these studies used both irradiation schemes within the same patient. UVB has a systemic effect on the body. Our hypothesis is that previous conclusions are incorrect and that the erythematogenic scheme will result in earlier clearance of the psoriasis.

109 psoriasis patients, referred for UVB phototherapy, participated in our study after given their written informed consent. After determining the minimal erythema dose (MED) patients were randomised in either group 1, erythematogenic scheme, or group 2, suberythematogenic scheme. Group 1 started with 70% of MED and every following irradiation with an increase of 40%. Group 2 started with 30% of MED and every next visit an increase of 20%. The study protocol was adjusted in case of erythema (sunburn) according to a standard erythema-phototherapy protocol, varying from skip one irradiation to lowering the percentage of increase. In case of clearance the study stopped. Clearance was defined as less than 10% of baseline body area of psoriasis.

Inclusion Criteria:

• Eligible for UVB phototherapy
• Older than 18 years

Exclusion Criteria:

• No topical medication for 2 weeks
• No systemic medication for 4 weeks
• No medication (betablocker, lithium) interfering with psoriasis