Lymphotoxin-producing human T-cell hybridomas are incubated in a medium containing phorbol myristate acetate, concanavalin-A or a mixture thereof, the resulting cells are fractionated by sucrose density-gradient centrifugation method to isolate a messenger RNA in 12.6S to 14.6S fractions, and a gene containing a part encoding a polypeptide having a lymphotoxin-activity is prepared from the messenger RNA. The gene is represented by the base sequence of the Table 1 as herein given. Using the present gene, a new lymphotoxin having the amino acid sequence (I) or (II) as given herein can be obtained by genetic engineering technology.