Background：An alternative approach to oral PUVA therapy for psoriasis, psoralen bath plus UVA therapy(bath PUVA therapy) that avoids the adverse effects associated with oral PUVA therapy has increasingly been used during recent years. Objective：This study was performed to evaluate the efficacy and safety of bath-8-MOP-UVA therapy in the treatment of psoriasis. Methods：Twenty patients were enrolled in this study after determination of the minimal phototoxic doses(MPD). We evaluated the total treatment number, duration, final UVA dose and total cumulative UVA dose of bath-8-MOP-UVA therapy to reach grade 4 response and categorized each patient into clearing, improvement, or failure groups based on the therapeutic efficacy. We measured the PASI score at two week intervals. Blood samples were obtained from all twenty patients 2 hours after bath-8-MOP and plasma levels of 8-MOP were quantified by a reverse phase high performance liquid chromatography. Results：The following results were obtained from this study. 1. Phototoxicity testing with bath-8-MOP-UVA elicited mean MPD value of 3.5±1.3J/㎠. 2. The mean PASI score at 10 weeks was significantly decreased to 5.8±1.3 from baseline PASI score 20.1±4.3. 3. Among 20 patients, clearing was shown in 13 patients(65%), 6 patients(30%) were improved and 1 patients(5%) showed failure. 4. In clearing and improvement groups, the mean treatment number, duration, final dose of UVA and total cumulative UVA dose reaching grade 4 were 19.3±5.4, 49.9±13.5days, 5.2±1.3J/㎠ and 68.6±30.1J/㎠, respectively. 5. Five patients experienced side-effects. Two patients had intense tan, one withdrawing because of it and the other continued treatment. Three had pruritus that was controlled on oral antihistamines. Phototoxic or other classic adverse effects of oral PUVA therapy, such as nausea, vomiting and headaches, were not observed in any of our 20 patients. 6. All twenty patients had an undetectable plasma 8-MOP level. The lower limit of detection level was 20ng/㎖. Conclusion：Bath-8-MOP-UVA therapy for psoriasis is a very effective and safe alternative to oral PUVA therapy. (Korean J Dermatol 2000;38(6)：756~761)