This is a combined Phase I/II non-randomized prospective study designed to determine the safety and assess the clinical efficacy of PDT in the treatment of oral leukeplekia with 5-ALA and 585-nm PDL with 1.5 ms pulse time. In the first part of the study we determined the maximum tolerated dose (MTD) of the PDL radiant exposure in combination with 5-ALA. In the second phase of the study, this dose is used to treat subjects at the MTD in order to determine the efficacy of the treatment by documenting the regression of the treated lesions.