Photodynamic therapy (PDT) is an experimental treatment modality for malignant tumours. The effect of PDT with haematoporphyrin derivative (HpD) was studied using a human bladder tumour (BL-17) which was implanted subcutaneously (s.c.) into immunodeficient Balb/c nude mice. This model is only suitable for short-term investigation of PDT because of the high mortality that arises due to the immune deficiency of the animals. In a short-term observation (2 weeks post-treatment), HpD sensitized PDT was effective in the control of tumour growth, with 71% of tumours cured. The effect of PDT was found to be highly dependent on doses of HpD and/or the activating laser light. The comparison of PDT effects of the gold metal vapour laser (GMVL) and argon ion pumped dye laser (AIPDL) indicated that no significant difference exists between these two different laser sources for PDT. The irradiation with laser light alone and the administration of HpD alone had no significant effect on tumour growth.