Abstract: Using a sensitive cytogenetic assay technique,the micronucleus test, we carried out a comparative study on the emergence rate of micronuclei among controls arid patients with psoriasis as well as pre-and post-treatment groups of psoriasis patients treated with photo-chemotherapy. The data obtained revealed that there was no statistically significant difference between psoriasis patients and controls, whereas the emergence rate of micronuclei in nucleated marrow cells of patients with posriasis was elevated following photo-chemotherapy, indicating that photo-chemotherapy might induce injuries to chromosomes in vivo,and might have mutagenic effects.