The fourth workshop on Mechanisms in B-Ce11 Neoplasia was held in Bethesda. Maryland. at the National Institutes of Health on March 24. 25 and 26. 1986. The meeting was attended by approximately 150 participants and 58 presentations were given. The purpose of these workshops and the yearly publications has been to provide a means for exchanging the rapidly developing information in this field and to bring maJor problems into focus. Edited trans- cripts of the 1983 and 1985 workshops were published by Editiones Roche Bas1e, Switzerland. Papers brought to the 1984 workshop were published in Current Topics in Microbiology and Immunology, Vol. 113. Numerous retrovira1 recombinant viral constructs are now in general use in a variety of test systems, both in vivo and in vitro. These are proving to have interesting bio10gica1-prQperties. ------- Kecent1y developed systems for inducing B cell tumors are described: 1) The development of spontaneous ~-ce11 tumors in transgenic mice carrying deregulated mlGBP genes and the Ig heavy chain promoter; 2) a method for inducing *p1asmacytomas in BAL~/c mice with short latent periods of ca 70 days by infecting pristane treated mice with retroviruses carrying various types of deregulated mlGBP genes; 3) induction of pre-B cell tumors with erbB containing recombinant retroviruses; 4) induction of B-ce11 and other tumors by infection of neonates with recombinant retroviruses. Several retrovira1 constructs containing mlGBP sequences do not induce B-ce11 tumors in pristane conditioned mice *.