Abstract: Objective To investigate the influence of Malassezia isolates that can cause hyperpigmentation or hypopigmentation in patients with pityriasis versicolor on the melanogenesis of B16F10 melanoma cells, and to detect the levels of cytokines associated with melanogenesis. Methods Primary culture of keratinocytes （1 × 106 cells/mL） derived from human prepuce were co-cultured with Malassezia strains isolated from hyperpigmented or hypopigmented lesions in the same patient with pityriasis versicolor, with the concentration ratio of keratinocytes to Malassezia cells being 1 ∶ 1, 1 ∶ 10, 1 ∶ 20 and 1 ∶ 30, respectively. The proliferation rate of keratinocytes was detected by MTT method. To observe the influence on B16F10 melanoma cells, five different types of culture supernatant were prepared, i.e. the supernatant from culture system of keratinocytes alone, supernatant from the coculture system of keratinocytes and Malassezia isolates from hyperpigmented sites or hypopigmented sites, and supernatant from keratinocyte culture in the presence of Malassezia cell-free supernatant from the culture medium of Malassezia strains from hyperpigmented or hypopigmented sites. ELISA test was performed in these supernatants to detect the levels of several cytokines associated with melanogenesis, including basic fibroblast growth factor （b-FGF）, endothelin-1, nerve growth factor （NGF）-β, IL-1α, IL-6, tumor necrosis factor （TNF）-α and stem cell factor （SCF）. B16F10 cells were cultured with the above 5 supernatants. After 48-hour culture, the proliferation rate of B16F10 cells was measured with MTT method, melanin content by NaOH assay, expression and activity of tyrosinase via Western blot and dopa-oxidase assay, respectively. Results The growth rate of keratinocytes was not affected by Malassezia （P > 0.05） when the concentration ratio of keratinocytes to Malassezia cells was more than 1:20. The melanin content, tyrosinase activity and expression of tyrosinase of B16F10 cells were increased in the presence of supernatant from co-culture of keratinocytes with Malassezia isolates from hyperpigmentated sites （P < 0.01）, while the supernatant from the co-culture of keratinocytes with Malassezia isolates from hypopigmentated sites showed the opposite effects on the above parameters. The proliferation rate of B16F10 cells had no obvious changes （P > 0.05） in the presence of supernatant from co-culture system. The level of endothelin-1 in the coculture supernatant of keratinocytes with Malassezia isolates was significantly higher than that in the culture supernatant of keratinocytes alone （P < 0.01）. Malassezia isolates from hypopigmented sites induced a higher level of secretion of endothelin-1 than those from hyperpigmented sites （P < 0.01）. Conclusions Malassezia isolates may influence the activity and expression of tyrosinase in B16F10 cells via the interaction with keratinocytes, resulting in subsequent regulation of the melanogenesis in these cells. Endothelin-1 might play a role in the hyperpigmentation caused by Malassezia in pityriasis versicolor.