Evaluation of the Suitability of PD P 506 A in the PDT of Distal Subungual Onychomycosis (DSO) of the Great Toenail.

Inclusion Criteria: * Male 18 - 75 years of age * Females up to an age of 75 years provided that they are postmenopausal, i.e. with spontaneous amenorrhea for at least 12 months or not of childbearing potential because of tubal ligation or hysterectomy * DSO of at least one of the great toe(s) affecting 20% to 60% of the target nail without spikes, confirmed before Visit 1 by at least one of the three methods: the methods of KOH test, periodic acid-Schiff (PAS) stain and mycology culture * The toenail infection can be due to a dermatophyte, yeast or mixed infections (dermatophyte and non-dermatophyte) * Toenails have to be cut regularly (indicator for existing growth) * Signed written informed consent Exclusion Criteria: * Patients with the target toenail involving the matrix (lunula) or having less than 2 mm clear (unaffected) nail plate length beyond the proximal fold * Presence of dermatophytoma (defined as demarcated and localised thick masses (≥ 3 mm) of fungal hyphae and necrotic keratin between the nail plate and nail bed) on the target nail * Other conditions than DSO known to cause abnormal nail appearance * Topical antifungal treatment of the nails within 1 month before PDT * Systemic use of antifungal treatment within 3 months before PDT * Patients who are unwilling to provide nail clippings * Patients who have been previously reported to be allergic against 5-aminolevulinic acid or other ingredients of PD P 506 A * Diagnosis of porphyria * Diagnosis of polyneuropathy * Dementia or psychic condition that might interfere with the ability to understand the study and thus give written informed consent * Simultaneous participation in another clinical study or participation in another clinical study in the 30 days directly preceding treatment