Abstract: The results of quantitative culture of Pityrosporum orbiculare/ovule (P.orb/ov) isolated from the lesions or healthy skin of the back of patients with psoriasis vuharis and pityriasis versicolor and normal volunteers werc reported.The mean number of spores/cm²(1952/cm²) and the activity of Pityrosporunt from the pabent with psoriasis vulgaris were significantly his,her than those of normal volunteers (mean number of spores 561/cm²),but not statistically different from those of pityriasis versicolor pabents (mean number of spores 3731/cm²).It suggests that Pityrosporu.m probably play certain role in the etiology of psoriasis.