The value of plasma concentration of 8-Methoxypsoralen(8-MOP) in the supervision of photochemotherapy has been recognized. However, plasma levels of 8-MOP were not proportionate to the degree of PUVA induced erythema and couldn't alone predict the degree of PUVA induced erythemal reaction. We made a speculation that the degree of PUVA induced erythema might correlate better with skin tissue levels of 8-MOP than plasma levels. Suction blister fluid(SBF) has been known to represent tissue fluid in the skin. So we per-formed a study of comparison of 8-MOP concentrations in both plasma and SBF.

Our purpose was to evaluate the correlation of the concentrations of 8-MOP in plasma and SBF 2 hours after oral administration of 0.6 mg/kg of 8-MOP.

Twenty six patients, aged between 16 and 50 years, undergoing suction blister surgery for vitiligo treatment, participated in this open study. Single oral doses of 0.6 mg/kg of body weight of 8-MOP were taken. Blood samples(5ml) and SBF(2ml) were collected at 2 hours after the drug administration, and 8-MOP concentration in plasma and SBF were quantitated by reverse phase high-performance liquid chromatography (HPLC).

8-MOP concentrations in plasma and SBF ranged from 18 to 545 ng/ml and 8 to 179 ng/ml, respectively. On the analysis of linear regression, a close-relation could not be observed between two SBF levels; measured and predicted values which were calculated from measured plasma and SBF concentrations (r'=0.583, P < 0.001).

The correlation of plasma and SBF concentrations of 8-MOP is weak. So, SBF levels of psoralen are recommended for the study of PUVA erythemal reactions.