We show that SV40 infection of human mesothelial cells directly causes overexpression of Notch-1, a key cell regulatory gene. Notch-1 induction is achieved at the transcriptional level and requires both the SV40 large T-antigen and the small t-antigen. Notch-1 upregulation is maintained in SV40-transformed human mesothelial clones and in SV40-positive mesotheliomas and derived cell lines. Activation of Notch-1 promotes cell cycle progression and it is required for the growth of SV40-transformed mesothelial cells. Our finding is relevant to the process of SV40-mediated human cell transformation, an effect that cannot be accounted for solely by SV40-Tag inhibition of Rb and p53.