Eighty basal cell carcinomas (BCCs) in 21 patients, 10 lesions of Bowen's disease in three patients, and four lesions of cutaneous T-cell lymphoma in two patients, were treated with photodynamic laser therapy (PDT), using topical application of the haem precursor δ-amino levulinic acid (ALA). The diagnoses were confirmed histologically prior to treatment. Fifty-five of the BCCs were superficial lesions, and 25 were nodular. Of the 80 BCCs, 39 (49%) were located on the trunk, 36 (45%) on the head and neck region, four (15%) on the leg and one on the arm. The two principal locations of the 10 Bowen's disease lesions were the leg (50%) and the trunk (40%). The T-cell lymphoma lesions were located on the shoulder and on the arm. A water-in-oil based cream containing 20% ALA was applied to the lesions, with a margin of about 10–20 mm beyond the visible tumour border, 4–6 h before the laser procedure. During this period of time the highly fluorescent and photodynamically active substance protoporphyrin IX (Pp IX) is synthesized via the haem cycle. Laser-induced fluorescence (LJF) was used for real-time monitoring of the Pp IX distribution in the tumour and in the normal surrounding skin, before and after treatment in all patients. Before laser treatment the Pp IX distribution demonstrated by LJF showed a demarcation between tumour and normal skin of about 15:1 for BCC and Bowen's disease, and 5:1 for T-cell lymphomas. Laser light from a pulsed frequency- doubled Nd: YAG laser pumping a dye laser with light emission at 630 nm was used for the therapy. The power density in the irradiation was kept below 110 mW/cm2, in order to avoid hyperthermal effects. A total energy of 60 J/cm2 was delivered for 10–20 min, depending on the tumour size. A complete response rate of 100% in superficial BCCs and 64% in nodular BCCs occurred after a single laser treatment, and a response rate of 100% was achieved after one additional treatment in the nodular BCCs. In the Bowen's disease lesions a complete response of 90% was obtained with a single treatment. Two of the four T-cell lymphomas resolved completely. The follow-up time was between 6 and 14 months.