PURPOSE: To produce the titled substance in large amount, by carrying out plasmogamy of animal cells capable of producing a bioproducing substance such as insulin, interferon, etc. e.g. pancreatic Langerhans' islands B cell, leukocyte cell, etc., with highly proliferative cell by the use of a cell-fusion inducing agent.

CONSTITUTION: Animal cell capable of producing a bioproducing substance such as insulin, interferon, growth hormone, adrenocorticotropic hormone, thyrotropin, somatostatin, lutenizing hormone-releasing hormone, glucagon, etc., e.g. Langerhans' islands B cell of human, pig, or cattle pancreas, human leukocyte cell, pituitary gland cell, hypothalamus cell, Langerhans' islands A cell, etc., is subjected to plasmogamy process with a highly proliferative cell, e.g. cancer cell, fetal cell, Eumycetes, etc. by the use of a plasmogamy inducing agent such as Sendai virus, polyethylene glycol, etc. The objective bioproducing substance can be produced in high amount taking advantage of the high proliferation function of the hybrid cell thus obtained.