Detection of HTLV-I proviral sequences in CD30-positive large cell cutaneous T-cell lymphomas. To investigate the possibility that cutaneous T-cell lymphomas of large cell type may be associated with human T-cell leukemia/lymphoma virus type I infection in nonendemic regions, tissue samples from six cases of large cell cutaneous T-cell lymphoma and four cases of small cell cutaneous T-cell lymphoma were screened for the presence of integrated proviral human T-cell leukemia/lymphoma virus type I DNA. Combined use of Southern blot hybridization and enzymatic DNA amplification revealed human T-cell leukemia/lymphoma virus type I-specific sequences in all cases of large cell cutaneous T-cell lymphoma and in none of the cases of small cell cutaneous T-cell lymphoma. These results suggest that in nonendemic areas, a significant proportion of large cell cutaneous T-cell lymphoma cases are associated with human T-cell leukemia/lymphoma virus type I. 